A character has a touchstone feat, and is currently attuned to random location A
This character is also a chameleon, and uses his bonus feat to take touchstone again.
This attunes him to random location A and random location B.
Now, if he attuned himself to random location C, he'd be able to choose whether he lost A or lost B. That's explicit.
There isn't anything linking a particular site to a particular version of the feat - each touchstone feat gives you a slot, so it looks like if he chooses a different bonus feat the next day, he can say "screw A, I'm keeping B", and keep B.
I guess the question here is
Q)Can a chameleon use his bonus feat to shuffle around a different touchstone feat's target?