This tattoo replaces mp_gunrunning_tattoo_001 (crossed rifles) for MP Female (not tested on male character)
-Click Edit Mode
-Navigate to GTA\Grand Theft Auto V\mods\update\x64\dlcpacks\mpgunrunning\dlc.rpf\x64\models\cdimages\mpgunrunning_ped_mp_overlay_txds.rpf\
-Make a backup if you want. There’s also a backup file included in the archive.
-Drag’n’drop the file mp_gunrunning_tattoo_001.ytd from the archive into here.
Backupfile, instruction, screenshots, all in the download.