FWIW - Installing Additional Party Skins

[Wyers]

After deleting Party and the relevant registry keys I installed Empire. Once Empire was installed I went in to look for the UCID key and it had not returned. Note that I did not rename any folders, I deleted everything.

Try the same steps replacing the relevant "Party" searches with "Empire".
I'm assuming it would be the same going from Empire to Party but I couldn't tell you for sure.

Let us know how it works.