There's no substitute for using the correct tool. I'd never take a pair of locking pliers to any firearm unless it wasn't mine and I didn't give a damn.
BTW the bushings on new Colts are staked in place. Be careful how you remove them so you don't muck up the threads. The other thing to remember is that the grip screw bushings are made butter-soft. It won't take much to deform them, so don't bother trying to re-use them afterwards. Make sure you order a set of brand-new bushings when you order the tool mentioned above.