1 - Open OpenIV and enable Edit Mode
2 - Navigate to GTA V/update/dlcpacks/mppatchesng/x64/models/cdimages/mppatches_p.rpf
3 - Depending on which character you want to change the mask for, either go into:
    - player_zero_p (Michael)
    - player_one_p  (Franklin)
    - player_two    (Trevor)
4 - Place the modded file