diff --git a/UnitTest/UnitTest.cpp b/UnitTest/UnitTest.cpp
index 96add941b..ea4c5718f 100644
--- a/UnitTest/UnitTest.cpp
+++ b/UnitTest/UnitTest.cpp
@@ -8,6 +8,8 @@
 TEST_MODULE_INITIALIZE(methodName)
 {
     // module initialization code
-    nitf_PluginRegistry_PreloadedTREHandlersEnable(NRT_TRUE);
+    //nitf_PluginRegistry_PreloadedTREHandlersEnable(NRT_TRUE);
+    _putenv("NITF_PRELOADED_TRE_HANDLERS_ENABLE=default");
+
     nitf::Test::j2kSetNitfPluginPath();
 }
\ No newline at end of file
diff --git a/modules/c/nitf/include/nitf/PluginIdentifier.h b/modules/c/nitf/include/nitf/PluginIdentifier.h
index 125ccd902..4f025bc58 100644
--- a/modules/c/nitf/include/nitf/PluginIdentifier.h
+++ b/modules/c/nitf/include/nitf/PluginIdentifier.h
@@ -70,7 +70,7 @@ typedef struct _nitf_TREPreloaded
     const char* name;
     NITF_PLUGIN_INIT_FUNCTION init;
     NITF_PLUGIN_TRE_HANDLER_FUNCTION handler;
-    NITF_BOOL enabled; // most preloaded TREs are disabled by default
+    int enabled; // most preloaded TREs are "not set" (disabled) by default
 } nitf_TREPreloaded;
 
 /*
diff --git a/modules/c/nitf/source/PluginRegistry.c b/modules/c/nitf/source/PluginRegistry.c
index e675d5360..992cccd7a 100644
--- a/modules/c/nitf/source/PluginRegistry.c
+++ b/modules/c/nitf/source/PluginRegistry.c
@@ -522,7 +522,7 @@ nitf_PluginRegistry_loadPlugin(const char* fullName, nitf_Error* error)
     nitf_Utils_baseName(keyName, fullName, NITF_DLL_EXTENSION);
 
     /* Now init the plugin!!!  */
-    ident = doInit(dll, keyName, error);
+   ident = doInit(dll, keyName, error);
     return insertPlugin_("Successfully loaded plugin: [%s] at [%p]\n",
         reg, ident, dll, error);
 }
@@ -971,8 +971,59 @@ insertCreator(nitf_DLL* dso,
 
 // Somebody might want to use a different set of preloadedTREs, or we might even want multiple
 // sets of preloaded TREs.  There's nothing to support either of those right now, but it's easy enough
-// to put the infrastructure in place to make it easy to hook-up.
-extern nitf_TREPreloaded defaultPreloadedTREs[];
+// to put the infrastructure in place.
+static nitf_TREPreloaded* getPreloadedTREs(const char* name)
+{
+    // Convert a name (e.g., "default") to a set of preloaded TREs.
+    // Only "default" is currently supported; see TREs.c
+    if (strcmp(name, "default") == 0)
+    {
+        extern nitf_TREPreloaded defaultPreloadedTREs[];
+        return defaultPreloadedTREs;
+    }    
+    return NULL;
+}
+
+static void enable_notset_TREs(nitf_TREPreloaded preloadedTREs[], NITF_BOOL enable)
+{
+    // NITF_PRELOAD_TRES is set, update all TREs which haven't been touched
+    for (size_t i = 0;; i++)
+    {
+        const char* pKeyName = preloadedTREs[i].name;
+        if (pKeyName == NULL) // end of list
+        {
+            return;
+        }
+        if (preloadedTREs[i].enabled < 0) // default is -1 "not set"
+        {
+            preloadedTREs[i].enabled = enable;
+        }
+    }
+}
+static nitf_TREPreloaded* getNitfPreloadedTREs(const char* name)
+{
+    // If NITF_PRELOADED_TRE_HANDLERS_ENABLE is set to *name*", we'll preload those TREs.
+    // This will NOT override a call to nitf_PluginRegistry_PreloadedTREHandlersEnable();
+    // by default, the `enabled` status of TREs is set to -1 "not set."
+    const char* envVar = getenv("NITF_PRELOADED_TRE_HANDLERS_ENABLE");
+    if ((envVar != NULL) && (strcmp(envVar, name) == 0))
+    {
+        nitf_TREPreloaded* preloadedTREs = getPreloadedTREs(name);
+        if (preloadedTREs != NULL)
+        {
+            enable_notset_TREs(preloadedTREs, NRT_TRUE /*enable*/);
+            return preloadedTREs;
+        }
+    }
+
+    // Enviroment variable not set (or not set to *name*), return preloaded TREs as-is.
+    return getPreloadedTREs(name);
+}
+static nitf_TREPreloaded* getDefaultPreloadedTREs()
+{
+    return getNitfPreloadedTREs("default");
+}
+
 static nitf_TREPreloaded* findPreloadedTRE_(nitf_TREPreloaded preloadedTREs[], const char* keyName)
 {
     if (preloadedTREs == NULL)
@@ -1000,9 +1051,14 @@ static nitf_TREPreloaded* findPreloadedTRE_(nitf_TREPreloaded preloadedTREs[], c
 static const nitf_TREPreloaded* findPreloadedTRE(nitf_TREPreloaded preloadedTREs[], const char* keyName)
 {
     const nitf_TREPreloaded* retval = findPreloadedTRE_(preloadedTREs, keyName);
-    if ((retval != NULL) && (retval->enabled))
+    if (retval != NULL)
     {
-        return retval;
+        if (retval->enabled < 0)
+        {
+            return NULL; // "not set" == disabled
+        }
+        const NRT_BOOL enabled = retval->enabled ? NRT_TRUE : NRT_FALSE;
+        return enabled ? retval : NULL;
     }
     return NULL;
 }
@@ -1010,10 +1066,15 @@ static const nitf_TREPreloaded* findPreloadedTRE(nitf_TREPreloaded preloadedTREs
 static NITF_BOOL PreloadedTREHandlerEnable(nitf_TREPreloaded preloadedTREs[],
     const char* keyName, NITF_BOOL enable)
 {
+    if (preloadedTREs == NULL)
+    {
+        return NRT_FALSE;
+    }
+
     nitf_TREPreloaded* result = findPreloadedTRE_(preloadedTREs, keyName);
     if (result != NULL)
     {
-        result->enabled = enable;
+        result->enabled = enable ? NRT_TRUE : NRT_FALSE;
         return NRT_TRUE;
     }
     return NRT_FALSE;
@@ -1021,7 +1082,7 @@ static NITF_BOOL PreloadedTREHandlerEnable(nitf_TREPreloaded preloadedTREs[],
 NITFAPI(NITF_BOOL)
 nitf_PluginRegistry_PreloadedTREHandlerEnable(const char* keyName, NITF_BOOL enable)
 {
-    return PreloadedTREHandlerEnable(defaultPreloadedTREs, keyName, enable);
+    return PreloadedTREHandlerEnable(getDefaultPreloadedTREs(), keyName, enable);
 }
 
 static void preloadedTREHandlersEnable(nitf_TREPreloaded preloadedTREs[], NITF_BOOL enable)
@@ -1038,14 +1099,13 @@ static void preloadedTREHandlersEnable(nitf_TREPreloaded preloadedTREs[], NITF_B
         {
             return;
         }
-
-        preloadedTREs[i].enabled = enable;
+        preloadedTREs[i].enabled = enable ? NRT_TRUE : NRT_FALSE;
     }
 }
 NITFAPI(void)
 nitf_PluginRegistry_PreloadedTREHandlersEnable(NITF_BOOL enable)
 {
-    preloadedTREHandlersEnable(defaultPreloadedTREs, enable);
+    preloadedTREHandlersEnable(getDefaultPreloadedTREs(), enable);
 }
 
 /*
@@ -1067,7 +1127,6 @@ static const char** preload_doInit(NITF_PLUGIN_INIT_FUNCTION init, const char* p
 static NRT_BOOL preloadTRE(nitf_TREPreloaded preloadedTREs[],
     const char* keyName, nitf_Error* error)
 {
-    const char** ident;
     nitf_PluginRegistry* reg = nitf_PluginRegistry_getInstance(error);
 
     /*  Construct the DLL object  */
@@ -1087,7 +1146,7 @@ static NRT_BOOL preloadTRE(nitf_TREPreloaded preloadedTREs[],
     dll->dsoMain = (NRT_DLL_FUNCTION_PTR)plugin->handler;
 
     /* Now init the plugin!!!  */
-    ident = preload_doInit(plugin->init, keyName, error);
+    const char** ident = preload_doInit(plugin->init, keyName, error);
     return insertPlugin_("Successfully pre-loaded plugin: [%s] at [%p]\n", reg, ident, dll, error);
 }
 
@@ -1173,7 +1232,7 @@ nitf_PluginRegistry_retrieveTREHandler(nitf_PluginRegistry* reg,
                                        int* hadError,
                                        nitf_Error* error)
 {
-    return retrieveTREHandler(defaultPreloadedTREs, reg, treIdent, hadError, error);
+    return retrieveTREHandler(getDefaultPreloadedTREs(), reg, treIdent, hadError, error);
 }
 
 NITFPROT(nitf_CompressionInterface*)
diff --git a/modules/c/nitf/source/TREs.c b/modules/c/nitf/source/TREs.c
index c8cbf1825..8ac463b98 100644
--- a/modules/c/nitf/source/TREs.c
+++ b/modules/c/nitf/source/TREs.c
@@ -105,7 +105,7 @@ static nitf_TREHandler* TEST_PRELOADED_DES_handler(nitf_Error* error) {
 /******************************************************************************/
 
 #define NITF_preload_TRE_(Tre_, enabled_) { #Tre_, Tre_##_init, Tre_##_handler, enabled_ }
-#define NITF_preload_TRE(Tre_) NITF_preload_TRE_(Tre_, NRT_FALSE /*enabled*/)
+#define NITF_preload_TRE(Tre_) NITF_preload_TRE_(Tre_, -1 /*not set*/)
 
 nitf_TREPreloaded defaultPreloadedTREs[] = {
     // Not preloading any TREs right now: with the existing system,
@@ -122,7 +122,9 @@ nitf_TREPreloaded defaultPreloadedTREs[] = {
     NITF_preload_TRE(JITCID),
     NITF_preload_TRE(PTPRAA),
     NITF_preload_TRE(RPFHDR),
+    NITF_preload_TRE(XML_DATA_CONTENT),
 
+    //NITF_preload_TRE(TEST_DES), // This should ALWAYS come from the DLL/SO
     NITF_preload_TRE_(TEST_PRELOADED_DES,  NRT_TRUE /*enabled*/),
 
 	{ NULL, NULL, NULL, NRT_FALSE } // end of list
diff --git a/modules/c/nrt/include/nrt/Types.h b/modules/c/nrt/include/nrt/Types.h
index 5788684fa..58a2a2420 100644
--- a/modules/c/nrt/include/nrt/Types.h
+++ b/modules/c/nrt/include/nrt/Types.h
@@ -159,9 +159,13 @@ typedef int nrt_CreationFlags;
 
 #define NRT_SUCCESS  (1)
 #define NRT_FAILURE  (0)
-#define NRT_TRUE     (1)
-#define NRT_FALSE    (0)
-
+#ifdef __cplusplus
+    #define NRT_TRUE     (true)
+    #define NRT_FALSE    (false)
+#else
+    #define NRT_TRUE     (1)
+    #define NRT_FALSE    (0)
+#endif
 
 #if defined(__cplusplus) && !defined(SWIGPYTHON)
 // "enum class" for C++ w/o SWIG