Hi guys, I wrote a small script based on a Mathoudebine work.
This script parses the .data theme and extracts the PNG files used inside. You can then edit those images in any image editor or replace them entirely. Save the image(s) you want to replace with a _mod suffix (e.g., theme_res_2646.png to theme_res_2646_mod.png) and use the script to repack them into a new copy of the .data theme.
To run the tool, install Python and put the script and the .data file(s) in the same folder. Inside that folder, run python theme-tool.py themename.data
Maybe some of you might find it useful 🙂 It should work for other displays as long as they use the same .data format as the 3.5-inch display.