I am not sure if this will work but the .c3p files is pretty much a compressed file, you can unzip that file, there is a layout folder that contains all the layout json files, if you find all the layout.json files that has the tilemap instance, you might be able to go in change the value.
after you modified the json, you have to zip the project back up and change the extension to .c3p and try and import the project from the file. i tried this with a very simple project and it worked. if you have multiple instances of the tile map in different layouts it might be a bit more work.