[Tamer]

It's for ZCMD, I don't know what command processor you are using, but here's the main idea.

pawn Code:

new Enabled[MAX_PLAYERS];

CMD:duty(playerid,params[])
{
    if(Enabled[playerid] == 0)
    {
    Enabled[playerid] = 1;
    SendClientMessage(playerid,-1,"You are on duty now!");
    // rest of the code
    return 0; // return 0, so the code will ignore the other lines, allowing you to go on duty.
    }
    if(Enabled[playerid] == 1)
    {
    Enabled[playerid] = 0;
    SendClientMessage(playerid,-1,"You are now off duty!");
    //rest of code
    }
    return 1;
}