Can a college or university withhold your degree for non payment and change your degree?
Yes, as you say, it is common that a university will refuse to issue a diploma or transcripts until you have paid them what you owe.

However, I've never heard of them making you take more classes if requirements change in the meantime.  Most universities have a policy that what you have to fulfill are the requirements as they were listed in the catalog of the year that you first entered the university / degree program.  The university can't change them retroactively.

But you'd better read your university's policies to be sure.  This should be explained in the course catalog.