The 24M does not need an inching pedal because it has a torque converter. It's the only grader in the Cat product line that has one. All other graders are direct drive which is why they need an inching (clutch) pedal to get the going and to get it stopped. The 24M can be directionally shifted at anything up to full engine RPM simply by flipping the directional shift control from F->R or vice versa, the converter takes care of the rest.
Regarding the smaller M Series without a converter (everything EXCEPT the 24M then) this is what the Operator Manual says about directional (shuttle) shifting.
To perform a shuttle shift, simply select the opposite direction from the current selection on the transmission control switch . The direction change must be done in one continuous motion, the transmission control switch should not be in the NEUTRAL position for greater than 0.2 seconds. If a shuttle shift is requested while operating in a gear higher than those described in the table above, the transmission controller will automatically downshift to a gear in the range of a shuttle shift.
What the table says is that in 1st speed to 3rd speed directional shifts F->R & R->F can be made at anything up to full engine RPM, in 4th speed the engine speed must be less than 1500RPM. Directional shifting is not recommended in anything above 4th speed, but as per text above the transmission will actually downshift to a gear where a shuttle shift is permitted before performing the shift.