Das machst du einfach ungefähr so:
new State = 0;
new Text:TD_Info;
///////////////////////////////////////
TD_Info = TextDrawCreate(...);
///////////////////////////////////////
SetTimer("ChangeText",30000,true);
///////////////////////////////////////
forward ChangeText();
public ChangeText()
{
if(State == 1) State = 0;
else State = 1;
if(State == 1) TextDrawSetString(TD_Info,"Servername: SERVER_NAME");
else TextDrawSetString(TD_Info,"Version: SERVER_VERSION");
}