once CApture Fit is established it is set in the PART. So any time you place this part in the future Capture Fit will be active.
It is NOT related to the assy!
But we copy our parts from the library to a project folder (i know, but...) So my question is, can i add relations to thet library part, or do i have to do it again each new project?
so in coping, I assume you then have two unique instances of the part...
Each would then act indipendantly of the other... The only way to add capture fit relations is thru an assy... that doesnt have to be a "good" assy but you can add relations in your library part byt creating a dummy assy or just palicng in a new assy to edit the capture fit relations.
This is pretty straight forward. You will probably understand best by just testing on a part to test the behaviour you desire...
im not sure the exact action that cancel Capture fit at placement ... but yes.. at placement the capture fit activates by default unti its canceled... again, in mot sure which action all cancel the defaul capture fit placement though