I am afraid I do not have a concrete answer but am posting with whatever information I have which might not be very helpful.
That said, I also feel sympathy towards your situation being an international student myself.
From my experience of being in undergrad student here ins US. I think you have a right to switch schools whenever you want. It is common for people to switch schools after 1 yr or semester. However, since you might run into a situation where you will have to switch before you come over, you might have some immigration issues. I am guessing you might have to ask the us embassy to issue you a new copy of your visa indicating the new school you are attending.
From my experience, the school you are attending should help you stay informed on such issues. Also, don't bother asking the international student advisor at the school you are declining for help, they will just ignore you. But do ask the other schools who you are waiting to hear form, let them know your situation and they must be able to give you some tip.
Here is my tip: Get a i:20 when you can, apply for a visa, if you get a new i:20 before your interview you should be fine, if after the new schools and the consulate should be able to help you.
About your thought on making a bad impression about students from your country. It is very likely that professors will judge future applications based on their experience with students form the same region/country. But logically they should be able to understand (given the big brains they have). I advise you not to tell your i-20 issuing school about this whole plan until you are 200% sure you are going to switch. Once you have made your decision u should politely let them know and they will have to understand.
My best wishes for you.