Why do you want to change the handles? If one of the handles broke, or if you just want the experience, I'd say "go ahead". But I wouldn't invest a lot of time and effort into a set of Irwin chisels. They're decent chisels but not generally considered "top-of-the-line". It'd be something like over-improving a house in a bad neighborhood. You'll never get your money back.

You could purchase some older, good quality, chisels without handles - you'd get them at a discount because of the lack of handles. Swan, Whiterby and a few other makers would be good candidates.

Mike