Hey there!
I would like to custom the menu that pops up when you press the space bar but i can’t find a way to do it properly with the “Enable Customize” option. Is there another way?
Thank you very much! 
I don’t think you can hotkey the Spacebar. That is used as ‘Move’ for Clip brushes and Selection brushes.
edit: or maybe I misunderstood you…I don’t think you can customize that popup.
As zber2 says, you can’t customize the Quick Menu, and you can’t assign the spacebar to other things. What you can do is create a custom menu and assign a hotkey to that, so that it pops up at the cursor just like the Quick Menu.
Just to add to what Marcus said…
If you are not familiar with creating custom menu’s and assigning hotkeys, see Custom Interface and Hotkeys.
People buy cars. They can get many makes and models, colors, engines and transmission types. And these options normally add to the original price. Not too many want reverse where overdrive is. Happy ZBrushing.
Well I just wanted to add the automasking in this palet, that’s all 
it’s not possible to do it for some script either?