Wolfire Games Forums

I know this is a super late response (I don't frequent the forum) but yes it is possible, but a lot of work. If you need help with it I'd recommend you to join the Wolfire Discord and check out the Overgrowth Modding channel.

Just open them with a text editor and replace the file names.
You can use the Search & Replace function in editors to speed up the process.

Overgrowth is very picky with filenames and underscores are not accepted.

Try renaming all the files to alphanumeric with dashes.
rock_density.png -> rock-density.png

You need to update the file names inside the XML files too otherwise it won't work.