Unfortunately Clarisse has no built-in keyboard shortcut editor.
You can edit most of it manually through its python script files. 🙂

• You can find all menu command in the Program Files\Isotropix\Clarisse iFX 3.6 SP7\Clarisse\python\menus\main_menu folder.
• In each sub-folder (that’s the menu structure itself) you’ll find a _populate.py file.
• Open the file with a text editor. You can change or add shortcuts as you like (of course don’t use the same for different commands). Create a backup file from the original one.
• The pattern is the same for every command.
  For example (edit folder: _populate.py file):
  menu.add_command("Edit>Deselect All", "./deselect_all.py","alt+d", "Deselect all items")
  I added the alt+d shortcut between the previously empty third "" part.

Cheers, D