How to change FirstPersonCharacter's turn/look up speed on runtime?

Yes, that’s the solution.

First, I used the slider to adjust TurnRateBase and LookAtRateBase with the direct simple method. This way I’m adjusting player’s turn speed using the cursor keys, he might use them instead of the mouse.

Then, in theFirstPersonCharacter, I multiply the mouse input by thatTurnRateBase, but converted to its apropiate range. (rates are 5-50 corresponding to axis scaling between (0,2 and 1,2).

And that’s all.

Thanks ChasetoferBoi!