Materials in the object maker are Case Sensitive; a texture will not render if you write ThisTexture when it's actually called thistexture.
Or if you're trying to apply an image file to the material of a different size or set up... it's all very finnicky!
Lastly, it may not work if the texture image is now a .jpg when it was previously a .png, and vice versa.
I had luck retexturing the bones by just copy the default rock texture material line of code, and pasting it into my personal massive .material file (LedaMaterials.material) as a bone texture instead, then entered that onto whatever I needed it to be on. Just had to change the image file in the material code to the bone texture I wanted, with a new name. This may not work for all objects and I'm happy to help you if it doesn't, but--
Here's an example of what I meanOpened up Rock.material (I believe it's called) from the Rocks folder
Copied the first code starting from the opening and ending with the closing tag }
Next I grabbed a BoneTexture for example called BoneTexture.png and put it under My_objects. You can see here I have my own material file also under the same my_objects folder, which I just copy and paste in needed materials into. You can make your own by copying any ol' material file from the FH folder and renaming it!
Finally I just opened LedasMaterials.material and used the rock texture from before to paste it at the tippy top (it never matters where the code is pasted as long as it's not inside any other material lines or before another material files closing tag of } !)
And now I have a bone texture to render onto any ol thang.
If you've already tried that, still have issues, or are trying to work with a different material code, then just paste it below or PM me it and I'm happy to work and look at that one too, the above is more or less just a general fix!