I'm an international applicant and I'm not very familiar with the routines of admissions in United States. I was wondering if I get admitted from a university and accepting their offer and while trying to get F-1 visa for it, I get another admission from another university, would I be eligible to accept the admission offer of the latter university or not?
You are only allowed to accept admission at one university. As soon as you do so, you should contact all other universities to which you applied, and tell them you have chosen another school and are withdrawing your application.
If you accept admission at University X, then withdraw it and accept admission at University Y instead in the same year, it's considered unethical behavior, and Y might rescind your admission if they find out.
Most US universities use coordinated acceptance deadlines, so you should know exactly which schools have admitted you before you have to choose one.
I've asked this question from a university in U.S. and they provided me this answer:
This is probably do-able, but you would likely end up losing the deposit (if you made one) at the other institution.
Ethically, this might be a gray area. But that would be up to you to determine what you are comfortable with.
Another university said:
Yes, as long as you do withdraw from consideration to the other PhD program in March/April, then you would most certainly be eligible for our CS PhD program.
So I think however this is not very ethically a correct action but is not forbidden and those who have previously accepted an offer would have this chance to change their mind.