Is it possible to mod-in this rule?

[companion]

I'm trying to add following rule to the ECW module:

[A friendly non-light foot, if within 2 tiles range and in LOS of enemy non-light mounted, AND NOT within 2 tiles range and in LOS of friendly non-light mounted, may not move forward or backward, may turn on spot, may not initiate charge, and may not exert ZOC.]

Any tip on where to start looking?

Should I post the question on FOGM forum instead for better exposure?