No problem at all.
I would recommend that the first thing anyone does after an upgrade is check for any outdated templates and phrases and revert them.
That ensures you are running up to date software and will avoid any issues related to missing elements, broken styles, etc.
If you make a note of any template edits you make then it will obviously be easier and quicker to reapply them.
Using EXTRA.css for any custom css edits will also make your life a whole lot easier.