Edit: if I used test pipes instead of cats and just swapped them back when inspection time came around would I need a retune every time?

I would like to thank everyone for sharing information with me, I’m starting to understand everything now but I have one remaining question that’s been sorta answered. The tune as you said adds timing etc and just clears the code for the test pipes. If I have the tune on and take my test pipes off than put on cats than put the test pipes back on afterwards will that tune be unaffected (as if nothing ever was changed, check engine light will not come back on after the test pipes were reintroduced)? Hopefully that makes senseEdit: another way of the question that might make it more easy to understand is say I have a tune than I purchase a new part will that new part be at it’s full potential because of the pre existing tune or if adding a new part would it have to be retuned.