[EricH]

<R54> So that the maximum power level of every ROBOT is the same, motors and servos used on the ROBOT shall not be modified in any way, except as follows:
A. The mounting brackets and/or output shaft/interface of the motors may be modified to facilitate the physical connection of the motor to the ROBOT and actuated part.
B. The gearboxes for the Fisher-Price motors are not considered “integral” and may be separated from the motors.
C. The electrical input leads on the motors may be trimmed to length as necessary.
The intent is to allow teams to modify mounting tabs and the like, not to gain a weight reduction by potentially compromising the structural integrity of any motor. The integral mechanical and electrical system of the motor is not to be modified. Note that FIRST will not provide replacements for modified parts.

The only questions are, is machining the case a legal modification, and if it is, are you allowed to open the motor to do it? If it's to facilitate mounting, yes. Otherwise, no. As for the second part, it's anybody's guess.