AFAIK, MB has a path replacement setting which is applied only when exporting a playlist to an m3u copy:
Properties -> Tab "Library" -> section "playlists" -> "map base file paths in exported playlists"
But if you have a whole bunch of mpb playlists, I would rather use a batch replacement program like "Text Crawler Free" (or similar).
As for me, I find Text Crawler easy to use, and you can perform a "find" before the effective "replace". But first, make a backup copy of your collection of mpb files to be sure.