Modifying the Nose-Hoover thermostat

GROMACS version: 2021.1
GROMACS modification: Yes

Dear Gromacs Experts,

Could you give me a clue what source code files I must modify to obtain a Nose-Hoover
thermostat that adjusts velocities only in Y and Z directions and leaves the X components
of velocities, please?

Also, what is better to obtain a legal NVT or NPT ensemble:

  1. Completely neglect thermostating along the X direction.
  2. The X component of velocity correction, due to thermostating, to be transferred to Y and Z
    components?

The reason I’m asking is that I want to perform some electroosmosis MD simulations with the
electric field applied along the X direction and I do not want to interfere with the movement
of particles along this direction.

Best regards,
Dawid Grabarek