I've created a simple stream editor script that will replace the name Debian with Devuan in plain and compressed files. Maybe this could be used to post process man pages.

debian-to-devuan-sed

The problem with that would be that there are seemingly quite a number of man pages in Devuan that include sentences like the following:

This manual page was written for the Debian GNU/Linux distribution (but may be used by others), because the original program does not have a manual page. (man page of spell)

In these cases, "Debian" should be kept in place instead of being replaced with "Devuan".

One method of processing the man pages that need to be altered would be an interactive script going through all man pages step by step. Each time the string "Debian" is found, it would have to interrupt and print out the line that word is in as well as the preceeding and following lines to provide enough context. Then the user running the script would have to be asked to decide whether "Debian" should be replaced by "Devuan" in this particular case and press the respective key (y or n). The script would also have to log the changes made, so someone could proof-read them later. The log file could then also be used to automatically post-process known packages forked from Debian in ascii and beyond, provided that the original man pages haven't been changed (which would have to be checked).

The above may seem a little lowbrow, but I don't see any way all the necessary replacements could be made without human intervention.