* The player can interact with a NPC cloaked by cloakonnpc command (click, mob event..) but the NPC trigger area is disabled (= the OnTouch* part is disabled).
* The changes last until the player leaves the map, logs out, or the npc option is updated by disablenpc/enablenpc/hideonnpc/hideoffnpc/cloakonnpc/cloakoffnpc commands.
Thanks to @aleos89