Yes...disabling and enabling another theme will not reset any images in the theme you uses before.
What I do with themes that I have modified to my liking was save them to my computer.
SSH into device via USB(not wifi) with a tool like i-FunBox or iTools.
Navigate to var/stash/Themes.xxxxxx/ name of your theme.
Drag the theme's folder to you desktop.
Now your theme is saved to your computer with all modifications intact.
Should you have restore and re-jailbreak, just install WinterBoard, SSH back into var/stash/Themes.xxxxxx, and drop your theme folder back into WinterBoard.