When building sparc64 packages, I use a script that lets me reduce the time that a poudriere build takes.
The script prepareblacklist merges together several blacklist.* files into a single blacklist file. It deletes duplicates and also removes any ports that are listed in the various files but no longer exist in the default poudriere ports directory. The latter will save you from runs that abort during setup.
It is not generalized at all. I list it to see if there is any interest in doing so.
The files can be found here.