diff --git a/.github/actions/restore-node/action.yml b/.github/actions/restore-node/action.yml
index ec924e9c908..62754f63f93 100644
--- a/.github/actions/restore-node/action.yml
+++ b/.github/actions/restore-node/action.yml
@@ -14,6 +14,11 @@ inputs:
     required: false
     default: '0'
 
+outputs:
+  endo-branch:
+    description: 'The branch of Endo used (NOPE if no override)'
+    value: ${{ steps.endo-branch.outputs.result }}
+
 runs:
   using: composite
   steps:
@@ -98,14 +103,18 @@ runs:
           sudo apt-get update
           sudo apt-get install libbsd-dev
         fi
-        yarn install
         # Replace the Endo packages with the ones built from the checked-out branch.
         if test -e ~/endo; then
-          scripts/replace-packages.sh ~/endo
-          rm -rf ~/endo
+          scripts/get-packed-versions.sh ~/endo | scripts/resolve-versions.sh
         fi
+        yarn install
         mkdir -p node_modules/.cache/agoric
         date > node_modules/.cache/agoric/yarn-installed
+        if test -e ~/endo; then
+          # Remove traces of the redirected `yarn install`.
+          git restore package.json yarn.lock
+          rm -rf ~/endo
+        fi
       shell: bash
       if: steps.built.outputs.cache-hit != 'true'
     - name: yarn build
diff --git a/.github/workflows/test-all-packages.yml b/.github/workflows/test-all-packages.yml
index cbc6182f323..26a9d5c4cc1 100644
--- a/.github/workflows/test-all-packages.yml
+++ b/.github/workflows/test-all-packages.yml
@@ -464,6 +464,8 @@ jobs:
       - uses: ./.github/actions/restore-node
         with:
           node-version: ${{ steps.vars.outputs.node-version }}
+        id: restore-node
+      - run: echo "ENDO_BRANCH=${{ steps.restore-node.outputs.endo-branch }}" >> $GITHUB_ENV
       # END-TEST-BOILERPLATE
       - name: yarn test (SwingSet)
         if: (success() || failure())
@@ -504,6 +506,8 @@ jobs:
       - uses: ./.github/actions/restore-node
         with:
           node-version: ${{ steps.vars.outputs.node-version }}
+        id: restore-node
+      - run: echo "ENDO_BRANCH=${{ steps.restore-node.outputs.endo-branch }}" >> $GITHUB_ENV
       # END-TEST-BOILERPLATE
       - name: yarn test (SwingSet)
         if: (success() || failure())
@@ -553,6 +557,8 @@ jobs:
       - uses: ./.github/actions/restore-node
         with:
           node-version: ${{ steps.vars.outputs.node-version }}
+        id: restore-node
+      - run: echo "ENDO_BRANCH=${{ steps.restore-node.outputs.endo-branch }}" >> $GITHUB_ENV
       # END-TEST-BOILERPLATE
       - name: yarn test (SwingSet)
         if: (success() || failure())
@@ -592,6 +598,8 @@ jobs:
       - uses: ./.github/actions/restore-node
         with:
           node-version: ${{ steps.vars.outputs.node-version }}
+        id: restore-node
+      - run: echo "ENDO_BRANCH=${{ steps.restore-node.outputs.endo-branch }}" >> $GITHUB_ENV
       # END-TEST-BOILERPLATE
 
       - name: yarn test (SwingSet)
diff --git a/packages/SwingSet/test/test-xsnap-store.js b/packages/SwingSet/test/test-xsnap-store.js
index 83b5f51f2ee..3c015ab89d4 100644
--- a/packages/SwingSet/test/test-xsnap-store.js
+++ b/packages/SwingSet/test/test-xsnap-store.js
@@ -1,3 +1,4 @@
+/* global globalThis */
 import '@endo/init/debug.js';
 
 import { spawn } from 'child_process';
@@ -130,6 +131,13 @@ test('create SES worker, save, restore, resume', async t => {
  * They are also sensitive to the XS code itself.
  */
 test('XS + SES snapshots are long-term deterministic', async t => {
+  const ENDO_BRANCH = globalThis.process?.env?.ENDO_BRANCH;
+  if (ENDO_BRANCH && ENDO_BRANCH !== 'NOPE') {
+    t.log(`Skipping test on ENDO_BRANCH=${ENDO_BRANCH}`);
+    t.pass();
+    return;
+  }
+
   const db = sqlite3(':memory:');
   const store = makeSnapStore(db, () => {}, makeMockSnapStoreIO());
 
diff --git a/scripts/get-packed-versions.sh b/scripts/get-packed-versions.sh
new file mode 100755
index 00000000000..b1a173c5f5f
--- /dev/null
+++ b/scripts/get-packed-versions.sh
@@ -0,0 +1,39 @@
+#! /bin/bash
+# Usage: get-packed-versions.sh <WORKDIR>
+#
+# This script creates package tarballs in the specified workspace directory and
+# writes out information for resolve-versions.sh to update a destination
+# workspace to use them.  This is useful for testing changes to dependencies of
+# the destination repository.
+set -xueo pipefail
+
+WORKDIR=${1:-.}
+cd -- "$WORKDIR" 1>&2
+
+# Install and build the source directory.
+yarn install 1>&2
+yarn build 1>&2
+yarn --silent workspaces info | jq -r '.[].location' | while read -r dir; do
+  # Skip private packages.
+  echo "dir=$dir" 1>&2
+  test "$(jq .private < "$dir/package.json")" != true || continue
+
+  ##################
+  pushd "$dir" 1>&2
+
+  # Gather the metadata.
+  name=$(jq -r .name < package.json)
+  version=$(jq -r .version < package.json)
+  stem=$(echo "$name" | sed -e 's!^@!!; s!/!-!g;')
+  file="$(pwd)/${stem}-v${version}.tgz"
+
+  # Create the tarball.
+  yarn pack 1>&2
+
+  # Write out the version entry.
+  jq -s --arg name "$name" --arg file "$file" \
+      '{ key: $name, value: ("file:" + $file) }' < /dev/null
+
+  popd 1>&2
+  ##################
+done | jq -s from_entries
diff --git a/scripts/resolve-versions.sh b/scripts/resolve-versions.sh
new file mode 100755
index 00000000000..c654f3891c8
--- /dev/null
+++ b/scripts/resolve-versions.sh
@@ -0,0 +1,19 @@
+#!/bin/bash
+set -ueo pipefail
+
+# Accepts a dependency version map on stdin and updates the current
+# package.json's resolutions section to use the packages and versions from
+# the map.
+# This is useful for temporary bulk updates over all packages.
+
+DIR=$(dirname -- "${BASH_SOURCE[0]}")
+
+cd -- "$DIR/.."
+
+override=$(jq 'to_entries | map({ key: ("**/" + .key), value: .value }) | from_entries')
+
+PACKAGEJSONHASH=$(
+  jq --arg override "$override" '.resolutions *= ($override | fromjson)' package.json |
+  git hash-object -w --stdin
+)
+git cat-file blob "$PACKAGEJSONHASH" > package.json