noobzter003's post in @pk on/off in Towns (Latest Git) was marked as the answer
int atcommand_pkmode( const int fd, struct map_session_data *sd, const char *command, const char *message ) {
nullpo_retr(-1, sd);
if( map_getmapflag(sd->bl.m, MF_PVP) || map_getmapflag(sd->bl.m, MF_PVP) || map_getmapflag(sd->bl.m, MF_GVG_CASTLE) || map_getmapflag(sd->bl.m, MF_GVG_DUNGEON) ) {
clif_displaymessage(fd, "You can only change your PK state on non-PVP maps.");
return -1;
}
else if (!sd->state.pk_mode) {
sd->state.pk_mode = 1;
clif_displaymessage(sd->fd, "You are now no longer in PK mode.");
}
else {
sd->state.pk_mode = 0;
clif_displaymessage(sd->fd, "Returned to normal state.");
}
return 0;
}
