Now if you were to open up the snapshots (or individual XMP files, you didn't say what format your IPTC Stationery Pads were stored within) with a Unicode-savvy text editor and were careful to not change any XML markup, you could do a search and replace rather efficiently. You'd still need to open up the individual files in your editor. Some editors like BBEdit (macOS) allow you to do search and replace across a folder of files all at once.
-Kirk