I know this is an old thread but this was the first google search when I asked this same question for the same problem. I would like to add that if NONE of these solutions work for you ( as they didn’t for me) you can dig into your computer hard drive deep enough into the files for the theme itself and put your desired image in that folder. rename your desired image to whatever the name of the image used is. and boom its done. no coding required. the coding of the theme itself will not be altered at all.
DIRECTIONS:
all you have to do is search in your Mac Finder for the rapid weaver program > right click and select “show package contents” > open the contents folder > open the resources folder > scroll until you find the themes folder and open it > split and Tesla are in the “new themes” folder, but im sure this method would work for any stock image issue
On the theme file, right click and select “show package contents”> open contents folder> open images folder > drag and drop your desired image into the folder (your Mac may ask for verification) > delete the image CURRENTLY BEING USED that you want to replace > rename your desired image to the EXACT same name as the previous stock image
Boom you’re done. In my opinion this was the easiest and quickest option that doesn’t involve code that might not work between updates, as it didn’t work for me. I hope this is easy to follow. I’m not sure if rapid weaver exists for PC but it would be the same theory.
Thanks! Good Luck!