You're still not being clear. When you save it, it doesn't matter what library you save it into (as long as you save it into a loaded library). It does, however, matter that the name be different from any other png names in all loaded libraries.
After editing, and hitting RELOAD to reload your libraries, did you go into the Materials dialog and change the texture to reference the new file? If going for a LightWorks rendering, did you then click the "Match with Internal" button?
You can use any texture you want, so something mechanical is amiss, that's all.
😉
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB