The next higher gear can not be under load already, a cr500 you can not override 4th gear because when the trans is in 3rd gear it is transferring power from the clutch basket threw the gear for 4th
This means you would be trying to push a gear under load into the next gear which would not want to slide out.
The way a override works is 2 gears for example 1st&2nd gears end up being engaged at the same time, now most transmission would lock up if this was done but because the dogs on the gears get cut on the backside like a ramp instead of being squared that will keep the dog engaged during deceleration.
The ramp allows the lower gear (1st) to get pushed out as the speed increases from the higher gear (2nd).
The shift drum gets welded and grooved to allow 1st gear to stay in engaged but then also allow 2nd gear to engage, now once that happens 1st gear becomes back loaded but since the dogs are cut like a ramp on the back side the trans does not lock up but instead pushes 1st gear out of engagement.
The picture below shows the green and brown gears meshed, the green would have to slide into purple gear shown in the second.
On the 1st to 2nd and 2nd to 3rd gear shift no loaded gears are being moved by the shift drum.
