[Gammix]

Код:

public OnPlayerCommandRecieved(playerid, cmdtext[])
{
    if(Info[playerid][Jailed]==1)
    {
        if(!strcmp(cmdtext,"/pm") || !strcmp(cmdtext,"/a")) return 1;

        SendClientMessage(playerid,COLOR_RED,"ERROR, You are in jail.");
        return 0;
    }
    return 1;
}

This code simply dissables all commands except /pm and /a which would bypass the check and work from the main source of the cmd. You dont need to re write the cmd in this callback.
I dont think so you require anything else than this. sscanf dont work as string matching or maybe y_stringhash. Sscanf is just opposite of format.