Subtracting commissions during back testing!!

 
Is it possible to manipulate the ACCOUNT_BALANCE variable in any way (I've tried but keep getting errors when I compile, maybe I'm doing something wrong?)? If so, I can calculate and subtract the commission from my balance after every trade. If not does anyone have any way to account for commissions when backtesting? Thanks.
 
nameless nameless:
Is it possible to manipulate the ACCOUNT_BALANCE variable in any way (I've tried but keep getting errors when I compile, maybe I'm doing something wrong?)? If so, I can calculate and subtract the commission from my balance after every trade. If not does anyone have any way to account for commissions when backtesting? Thanks.
The backtest accounts for commission. You don't need to do it manually.