Is there a way to link a modded interaction to a certain trait myself using S3PE? IF so, how exactly do you do it?

Depends on what exactly you mean by link. If the interaction has ITUN, RequiredTrait and ExcludingTrait are valid fields to add.
The KnockDown_ActivityTable ITUN in EA's GameplayData is a good example of how how to use RequiredTrait.

And just for future reference, the Create forum is where those who know about creating and editing mods hang out. They might miss questions asked in general, but luckily I scan through each of the forums to catch em when I can