Will applying themes or changing compiz config settings or unity tweak tool settings or any other changes in Ubuntu 15.10 have any effect after upgrading to 16.04 in future?
I want to make my Ubuntu look like OSX Yosemite 10.10 and be sure that the changes will not be reverted once I upgrade to 16.04.
Nobody knows that. Anyway after upgrade to a new release you will have to redo it. And something may not work. Custom themes are not supported and nobody tests what happens after a release upgrade.
You should be able to use unity-tweak-tool and it should not cause missing files or crashes.
Although, you should backup all your theme files such as the launcher_bfb.png file as this file may be replaced by the default file if you upgrade in the future.
