Yes, it is.
For MR-J4-A/MR-J3-A, 
set by [Pr. PC13]. 
As the initial value (100.0%), the maximum torque is generated at ±8 V. 
To generate the maximum torque at ±5 V, 
change the setting to [Pr. PC13] = 160.0 (= 8 V/5 V*100.0)
. 
The parameter number, etc. may differ depending on the model. 
For details, refer to each servo amplifier instruction manual.