Whilst I don't know anything except the definition of String theory and I'm a beginner, I'm curious about it.
What I would like to know is: does string theory change a lot in Physics? If it's not true, what else would suffocate in Physics due to String theory? It's just an assumption and not some experimental observation, right?
A layman's explanation would be helpful!
OP wrote(v1):
Would string theory change everything? Does String theory change the whole Physics?
More generally, it seems OP is asking if a new theory would contradict old experimentally well-established theories?
No, the very first test of any new theory is if it can reproduce the old theories in their respective domain of experimental validity. If the new theory fail that test, it has hereby been falsified, and it must therefore be discarded.
Concerning experimental tests/signatures of string theory, see e.g. this and this Phys.SE post and links therein.
