You can strike clauses and file an amended agreement, they can refuse to accept such things; but you are not obligated to sign unless they are compensating you adequately for what you are giving up. Approach this as an equal; decide what _you_ are willing to put up with. Nobody on this forum can tell you what you can and cannot live with.
Do figure out your BATNA at this time.
So, if you are asked to sign one of these things either ask for some cash up front or hold in your back pocket that it's probably not enforceable (though it can certainly end in litigation which can be terrible for everyone involved).
In the US, at least in general, this is a contract, and without the employee getting "consideration" it's not valid. And mere continued employment doesn't count, they'd have to give you something extra such as a raise or bonus.