Yes. The first time after all screws are out, the two halves need some minor force to separate. Because the fan wires go to the back side, you don’t want to jerk it apart. It’s pretty straightforward in there. I’ve taken one down to just the screen left installed so I could paint one. Make sure your side roller knobs are facing out properly and centered when putting back together.
Not that I can see. The start/stop button is slaved to left stick throttle and shares that channel. The aux button is assigned to the last unused channel on the radio and is not linked to anything. There is no obvious way to change within channel settings. You could steal the button as hardware to save time ordering a new switch. Just swap out the red cover with the black and make the aux the dead switch. It’s useless anyway.
If there is a way to change it probably requires a hack in the android OS and radio app. That’s a level of skill I don’t have.