Hi all!
Luckily after 2 days the server decided to use the new code, so I don't need to restart anymore!

Thanks anyway for all the suggestions... finding a solution could be useful later on or for someone else!
@Jaid: I tried your method in my test environment but the behaviour seemed a bit random...
I removed the "cache settings for fast load" first, I changed the code under webapps/my-theme/css folder and nothing happened (normal).
then I renamed the folder WEB-INF as you said, but nothing happened... it did take the changes the second time I did the procedure, but BEFORE renaming it with the original name (??)
And also Firefox Chrome and IE were having different behaviours... of course I deleted the browser history everytime, but one would keep the old file, the other didn't...
I did this a couple of times and everytime it was doing different things...
@Adel: I modified the css under webapps (webapps/<your theme>), but I couldn't find the right thing to delete in the temp folder! my theme wasn't there