Sigh, seems I have forgotten some important things about decaling again:

I want to apply a bumpmap on a certain part of my charas body,

so I flattend that part in a on/off pose and made a new action activated that pose and wanted to apply new decal to that part,
but that option is not available there.

What am I doing wrong here?

Add decal to the model in the modeling window, but do not apply it. Then in the action go to muscle mode, double click the decal container in the PWS to show the image.

Or just right-click the model name in your project hierarchy while you're in the flatten pose/action and add a new decal from there.

Thanks a lot.
(Maybe this little incoherence in the interface could be altered in the future, if not to complicated...)