[R0FLC0PTER]

You could create a global variable at the top of your gamemode, somthing like this:

pawn Код:

new bool:AreCellsLocked = false;

Add a command to lock the cells

pawn Код:

if (!strcmp(cmdtext, "/lockcells", true))
{
    if (AreCellsLocked)
    {
        AreCellsLocked = false;
        SendClientMessage(playerid, COLOR_GREEN, "The celldoors have been unlocked!");
    }
    else
    {
        AreCellsLocked = true;
        SendClientMessage(playerid, COLOR_GREEN, "The celldoors have been locked!");
    }
}

And change your /exitcell command to this

pawn Код:

if(!strcmp(cmdtext, "/exitcell", true))
{             
    if (AreCellsLocked)
    {
        SendClientMessage(playerid, COLOR_RED, "The celldoors are locked, you can't exit now!");
    }   
    else if(IsPlayerInRangeOfPoint(playerid, 2, 350.8596,2044.6348,-15.8942))
    {
        SafeSetPlayerPos(playerid,350.8192,2043.3998,-15.8942);
    }
    else if(IsPlayerInRangeOfPoint(playerid, 2, 354.4935,2044.5579,-15.8942))
    {
        SafeSetPlayerPos(playerid,354.4162,2042.9690,-15.8942);
    }
    else if(IsPlayerInRangeOfPoint(playerid, 2,358.4893,2044.3650,-15.8942))
    {
        SafeSetPlayerPos(playerid,358.5545,2043.4036,-15.8942);
    }
    else if(IsPlayerInRangeOfPoint(playerid, 2,350.4196,2026.4515,-15.8942))
    {
        SafeSetPlayerPos(playerid,350.3955,2028.2583,-15.8942);
    }
    else if(IsPlayerInRangeOfPoint(playerid, 2,354.1672,2027.1947,-15.8942))
    {
        SafeSetPlayerPos(playerid, 354.1133,2028.2479,-15.8942);
    }
    else if(IsPlayerInRangeOfPoint(playerid, 2, 354.1672,2027.1947,-15.8942))
    {
        SafeSetPlayerPos(playerid, 354.1133,2028.2479,-15.8942);
    }
    else if(IsPlayerInRangeOfPoint(playerid, 2,358.3171,2026.7179,-15.8942))
    {
        SafeSetPlayerPos(playerid, 358.4237,2028.2480,-15.8942);
    }
    else if(IsPlayerInRangeOfPoint(playerid, 2,358.6216,2044.7598,-11.8717))
    {
        SafeSetPlayerPos(playerid, 358.6442,2043.2045,-11.9187);
    }
    else if(IsPlayerInRangeOfPoint(playerid, 2,354.5882,2044.3750,-11.8715))
    {
        SafeSetPlayerPos(playerid,354.5472,2043.2047,-11.9437 );
    }
    else if(IsPlayerInRangeOfPoint(playerid, 2,350.9304,2044.5676,-11.8759))
    {
        SafeSetPlayerPos(playerid,350.9572,2043.2021,-11.9185);
    }
    else if(IsPlayerInRangeOfPoint(playerid, 2,350.8673,2026.9972,-11.8690))
    {
        SafeSetPlayerPos(playerid,350.8806,2028.2472,-11.9185);
    }
    else if(IsPlayerInRangeOfPoint(playerid, 2, 354.3078,2026.9812,-11.8754))
    {
        SafeSetPlayerPos(playerid,354.2941,2028.2482,-11.9187);
    }
    else if(IsPlayerInRangeOfPoint(playerid, 2, 358.5276,2027.2445,-11.8175))
    {
        SafeSetPlayerPos(playerid,358.6219,2028.2504,-11.9187);
    }
    else
    {
        SendClientMessage(playerid,COLOR_GREEN,"You aren't near the cell.");
    }
    return 1;
}

Here i'm assuming you have COLOR_GREEN and COLOR_RED defined.
Note that the code is uncompiled and untested.

Please post your result.