according to the log its either freezing on shutting down one of the dsps you might have enabled or a plugin
Thanks a lot for taking a look! You're right, it was indeed one of my plugins causing this issue, the MusicbeeIPC plugin:
https://getmusicbee.com/forum/index.php?topic=11492.0Actually, when I tried to simply disable the plugin, MB shut down with the plugin panel frozen and I had to close the remaining MB process in task manager.
The disable action was succesful though and the error log showed the exact same numbers as when I had the issue with the skin change (latest nr = 11, instead of 14).
I can now change skins again and MB will restart without issue with the new skin loaded.
The MusicbeeIPC plugin hasn't been updated since 2013, so it's fair to say the issue lies with that plugin and not with MB 3.5
It's not even an issue for me, since I no longer require the functionality of MusicbeeIPC.