G'day folks.
I've had a look inside 1 of my spare controllers awhile ago with the same idea & I saw 2 issues with removing that circlip;
First is that it already takes a big twist on the twist grip to get full throttle. Pulling the brass slide further would take half a turn at least. You'd want to fit a race style quick action twist grip that may not look as pretty.
Second issue is that the brass pull shaft is attached to a flat slide with a V shaped slot in the end that varies the amount of light falling on one of two photo diodes next to each other, one for power mode, one for eco. If the flat slide is pulled too far out, it could jam, of course, wide open.
You could try bending the LED opposite the photo diodes slightly so the slot uncovers it earlier.
While you've got the controller open, you'll see a blue pot near the throttle pull shaft. As far as I can work out it varies the ramp up, making throttle response a little softer or snappier.
Have fun. I sure do with mine!
AussieRider