Wolfire Games Forums

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.