The Wagos are great for house wiring, much better than wire nuts. Not appropriate for use in an airplane. I think you are severely overthinking this. Wiring in the buzzer to your stall light is (IMHO) a simple minor alteration. You said you were getting your A&P involved, let them tell you how they want you to attach it and mount it, do that, have them look at it and get the log book sign-off. Then it's a permanent minor alteration, no violation of any rules. You don't need an STC or field approval or anything here (again, my opinion, your A&P could potentially have a different opinion, but nothing here falls under 43 Appendix A, etc), this is just a simple minor alteration made legal with a log book entry by your A&P. Trying to make this some "temporary" install isn't worth the mental gymnastics.