You can slide while holding onto the ceiling by jumping and pressing 'up'.About the remapping, if you ever have a problem with it, you can still use the mouse in the menu. Go to the remap using the mouse and remap again, hopefully it will work.
thanks , the mouse option in the menu wasnt working when i was trying but it is now
No problem. You can also slide while on the floor by pressing down. Thank you for playing!