Yes, it is possible to replace the CMOS battery in the PS 3 Super Slim.
Sadly, you will almost need to do a full disassembly of the device to get to it, so if you aren’t too confident with doing this or don’t have a T8 Torx Security Bit you should think twice before getting into it and make sure to have a T8 bit or screwdriver.
This video shows the disassembly process for the device, so if you want to try it out you may find it useful. https://www.youtube.com/watch?v=FI5HcIE2NNE
[video|https://www.youtube.com/watch?v=FI5HcIE2NNE]
Good luck and hope this helped! :D