I've successfully switched out some blades by clamping one of those trigger-type bar clamps (see image below) on the blade, letting the blade rotate to the point that the clamp was wedged against the baseplate, then applying the wrench.

Striking the wrench end a sharp blow with a moderate-weight hammer helps to get it started.

Hello, I have found that the ultimate tool for freeing up a blade bolt or star washer is an impact wrench with the appropriate size socket. Good luck, Lou

Bill, I like your solution a lot.  Of course I could put some wood in the jaws of my new Record vise (ahem) and clamp the blade in that.

I went back and looked at the first post here, and am mildly amazed that we built a two-page thread out of this:

Of course, we did digress a bit...