I figured I'd be clever and just change the heading field for the local player, in order to do instant turning. Well, it does turn my player around, but it keeps running in the same direction, so it looks like it's pirouetting and moonwalking while moving in a straight line.
Do I have to use TurnXXXXStart()/End() in order to make it work, or is there some other offset I should be changing? The property I'm writing to is at offset 0x848 in CGUnit_C.