My initial problem seems to be irrelevant. I did not understand what was meant by "throttle" which is more of an RC jargon misunderstanding than it is an issue with raspberry pi. (If you're looking for an answer this link shows it pretty well.)
Sorry for being off-topic! Sometimes it's hard to know when you are working from little experience. :)
The OP is worrying that if he turns the L298N driven motor by hand, will the "back power" generated fry his Pi？
The L298N already 8 flash back diodes (D1 to D8 in the picture below) to protect the power to the L298N motor driver, so there is no need to add the extra one.
(1) We need to know what is going on inside the L298N ...
The L298N module typically has a terminal marked +5V (shown as logic supply 5V on the attached diagram).
As long as you do not connect this terminal to the Pi you will be fine.
I am not going to speculate further without a clear photo of the module you are using.
The L298N module derives its logic supply power from the attached battery/power supply or the ...