If I had my guitar set up, and I change the strings (using the exact same size and brand) and I make sure the saddles don't move, then it will retain perfect intonation(or however perfect it was before I change them)?
Chances are your intonation will be nudged if your bridge saddles move, which they may do slightly anyway. But they won't move by much. Shouldn't take you more than 5 mins to check, 10 if they have slightly de-intonated. Try it and find out!