Leroux: ATTENTION! :)
Since the forum software has become even buggier in recent years, I don't dare to edit my original posts anymore, but there actually is a new and much easier way to apply hacked designs in FRUA now than the UAShell installation I described in 2015, at least for Windows, I guess. It's actually been available since 2017, and I overlooked it so far (my apologies!).
UA DESIGN APPLY by Donnie Ewald
uadap.zip Readme (Your anti-virus program may complain about it because it's a small unknown exe, but its fine, and my AVG gave me the okay after sending it to the test lab.)
How it works is you give it the path of your FRUA folder with the CKIT.exe in it and the folder of the design you wish to apply and press Apply, then exit and start FRUA. If you want to apply another design, you first press Revert to restore the original FRUA version, then Apply again with the path of your new design. Simple as that. Basically the same thing that UAShell did, but as a Windows program without complicated installation. (see screenshot)
Great alternatve.