I've followed the tutorial on how to export the palette in a plugin, here's my problem:
I created a new tool group for the CompositeStructureDiagram in wich I've added a Class ( I just selected the first one in the UML tool list), when I edit in the plugin I can't add the Class using the tool I created, but I can with the default one in Nodes.
yes I resolved this: when you create a new custom palette it's all right, BUT if you want to modify it, it's a little tricky due to what I think it's a bug.
When you modify an already created palette, in the uml tool list you see copies of the same tools, for example you can see 3 or 4 Class tool: this is because it show the tools you already created in the previous palette.
If you put one of these copies in your new palette, it won't work.