Any way to customize primsjs config?

[martypitt]

I'm trying to add a custom langauge spec into the prismjs config.

The docs for gatsby-remark-prismjs suggest I need to configure the languageExtensions.

However, gatsby-remark-prismjs is already configured in the gatsby-config.js:

const allGatsbyRemarkPlugins = [
<snip>
    {
      resolve: 'gatsby-remark-prismjs',
      options: {
        showLineNumbers: true
      }
    },
    ...gatsbyRemarkPlugins
]

Is there any way I can override or modify this definition from my own config, to pass in the custom config I need?