I would export the canonical_uri tiddlers to a JSON file and run a repeated text edit on them to change the code. Then import the new json file back into the wiki.
Sometimes I find it is easier to change the comma between fields into a tab and then import that file into a spreadsheet so you can manipulate the various columns. Export it as a SCV file and replace tabs with commas to get back to where you started.
As long as you keep the tiddlers’ titles the same, this will overwrite what is already there, maintaining any tags, fields, etc.
This is the code for my image tiddlers
As for different versions of image tiddlers, have a look at Fallback handling for $image widget. @EricShulman provided an edit for the $image widget that allows for fall back if the first location does not have the image to a second location. I use that for having a local Image directory and one on a server so that if the local directory is not available then it pulls the image out of the server copy.
This is how I configure the fallback location.
bobj