The difference is, I expect to use the objects many many more times than I edit them. Thus, a require plus the cost of file access once out of ten or more hits is probably more efficient than an eval on each hit.

Apache::Registry had a lot of good information in there... but they called a couple of mysterious XS functions in the mod_perl code itself, which is slightly beyond the scope of my project at this point. (Now I'm off to see if I can freeze an object, redefine part of its class, thaw it, and have everything work okay!)