I slipped this topic across to Development because we are moving out of support territory here. You need to just get going with creating the plugin or automation that does what you want. Let us know how you get on! If the features you add are more widely useful, they may be considered for inclusion eventually in core Discourse.
Refer to Documentation > Developer Guides and #community-wiki:developers for guidance on creating plugins.
You can also start more topics in Development to ask more questions, but I do recommend you have code to share as you do so. It is easier for others to help you if they can see what you’ve done so far.
Yes, invitation links are always unique.
I don’t know what you mean by “pass your filters and be added to the native Discourse source code”.
These are the types of questions I think you will be able to find out for yourself as you dig into the code.