I've been using the SHA1 hashes of my commits as references in documentation, etc. I've realized that if I need to rewrite those commits, I'll need to create a lookup table to correspond the hashes for the original repo with the hashes for the filtered repo. Since these are effectively UUID's, a simple lookup table would do.

I think that it's relatively straightforward to write a script to do this during a filter-branch run; that's not really my question, though if there are some gotchas that make it complicated, I'd certainly like to hear about them. I'm really wondering if there are any tools that provide this functionality, or if there is some sort of convention on where to keep the lookup table/what to call it? I'd prefer not to do things in a completely idiosyncratic way.