[Scenario]

pawn Код:

new szName[25];
GetPlayerName(playerid, szName, sizeof(szName));
new string[40];
format(string, sizeof(string), "[ADMIN]%s", szName);
SetPlayerName(playerid, string);

Use that for the first part. Untested.

And for the second, use this under OnPlayerConnect.

pawn Код:

new szName[25];
GetPlayerName(playerid, szName, sizeof(szName));
if(strfind(szName, "admin", true) != -1) Kick(playerid);

Untested. I may have messed up the strfind syntax- I don't use that function very often.