It would be a bit confusing then, I think, since the option for one feature would control another, plus the mode automatically changing if you tried to use a feature you didn't realise was turned off, or just accidentally typed a slash...
Additionally, not all regexp renames will use a slash at all (although that is rare it does still happen sometimes).
For something like that I would probably make a button or key which toggles an additional toolbar down the side of the window which has all the presets in it. I could then click each one of the presets and then a final button which closes the toolbar. Have a look at the Flat View Toolbar for an example of this.
Yup:
Rename PRESET=regexp