Scratch

You use:

ScratchFrameMorph readSkinFrom: (FileDirectory default directoryNamed: 'ScratchSkin')

Be sure to reload the whole frame, too (either by "Save image for end-user" or with the following)

World fullRepaintNeeded.
    viewerPane rebuildCategorySelectors.
    self updatePanes.
    self
        view: scriptsPane target
        tab: scriptsPane tabPane currentTab
        category: viewerPane currentCategory

In a menu item or block, or, you can put it in the workspace, highlight all of it, and click "Do it" or "Run" (I forget which).

In that case, there may be something wrong with the category selectors.

Try saving the image for end-user first, does that give you an error?

Hmm, I guess there's something wrong with my code, as I took it straight out of my own mod (where it DOES work). Maybe there's some other important code around it...

I'm pretty sure the code is:

ScratchFrameMorph readSkinFrom: (FileDirectory default directoryNamed: 'ScratchSkin')

Note: that code is the same as above.
However, the skin must be in the ScratchSkin directory (in the working directory of the mod), and (this is probably where it messed up) it must have everything that is needed.

And after trying that code, save image for end user.

Oh no! All the categories deleted, and it's stuck like that! O.O