This is potentially semantics, but arguably 'Bitcoin' (or at least the specific bitcoin you claim to 'own') is defined by the set of rules. Thus if someone adds another rule, they are not using the same 'Bitcoin' any more. In that sense you still control it, even if everyone moves to the 'new Bitcoin', though it will now be worthless.

This does happen in practise, it is what is known as a 'fork', and things can get complicated, because generally when the rules change most people will be able to control addresses on both sides of the fork, and more confusingly, it may be possible to 'transplant' transactions from one fork to another (i.e. if you start a transfer from address A to address B on one set of the rules, anyone can also initiate the same transfer on the other set).

Another point, more specific to the example you gave, is that within the rules of bitcoin, the 'miners' who verify the transactions with a proof of work are free to choose which transactions they include. If a sufficient percentage of them choose not to include transactions from a particular address, then it becomes much slower and/or more expensive to transfer anything out of them.