it doesn't rotate, its held on with a screw that goes thu the grip and bar. You may be able to adjust the the whole lot by loosening and then rotating the whole assembly not just the grip and switch gear.
the grip clips into the switch gear which in turn has a bolt straight through it and the bars...so to move the switch would mean drilling another hole for the bolt hole where my thumb is holding the grip back....
And the service manual says not to open the switchgear as there's a risk of damage to the sealed circuit boards. You'll need a T8 torx btw
Also, note there's a little plastic cover on the opposite side of the switch from the grip. Its held on by 2 tabs. Lift these and it'll pop off. You are then supposed to release the 2 mini wiring connectors to expose the end of the plastic grip tube tab. Press that and the grip should pop out assuming you have undone the bolt already mention in a previous post. You can then drill a new hole through the clip on, re-assemble and job done, you have now rotated the switch to a new position. Yeah, good luck, especially with those mini wiring connectors.
Probably best living with it!