[core] Allow external modification of packet guard allow list

[zach2good]

I affirm:

• I understand that if I do not agree to the following points by completing the checkboxes my PR will be ignored.
• I understand I should leave resolving conversations to the LandSandBoat team so that reviewers won't miss what was said.
• I have read and understood the Contributing Guide and the Code of Conduct.
• [lol, no] I have tested my code and the things my code has changed since the last commit in the PR and will test after any later commits.

What does this pull request do?

Helps with issue discussed in #1162

[github-actions]

✨ Thanks for the PR! ✨

This is a friendly automated reminder that the maintainers won't look at your PR until you've properly completed all of the checkboxes in the pre-filled template.

[TeoTwawki]

[lol, no]

dear contributors, do as i say not as I do. If you copy that on your PRs well..

[zach2good]

^ I wrote and designed all the involved systems entirely from scratch and I know exactly what I'm doing. Do as I say not as I do 😆.

I would love to be humbled by a very obvious mistake in this PR.

[TeoTwawki]