I don't know what code is under the hood but I think altering phent_setmaxvel may cause problems as it's used to stop the entity after it's reached a certain velocity. Altering it the way you suggest would change it's behavior for paramaters of 0,0,0 only and I'm not sure that's such a good idea. It would probably be easier and cleaner to add different behaviors via new functions as opposed to altering existing ones.

Regardless of what code is "under the hood" I think we are both interested in a quick function that simply resets the variables to zero WITHOUT unregistering the entity. This way when we apply forces via phent_addvelocity we will know there are no existing forces already there. Is my assumption correct, because clearvelocity() definatly sounds like what I need.