Unfortunately still (as of Prime 9) no way to customize keyboard shortcuts.
But you are lucky anyway because you obviously use an English system with an English keyboard. Those of us with foreign (from your point of view) language keyboard have the additional problem that many shortcuts given in the help an tooltip simply don't work the way they are shown. Some shortcuts can be found by trial and error, some seem simply be missing.
The global assignment you mention is said to be Ctrl-Shift-~ in my German Prime version, but actually is Ctrl-Shift-ö (this one was easy find with the help of a picture of an English keyboard). And yes, I agree that this keyboard short is rather awkward.
All in all a quite sloppy implementation - very annoying and a shame for a big company like PTC.
