Brunello is 100% Sangiovese. But to answer your question, no. As long as your sanitation and O2 control is good there shouldn't be a problem.
Which grapes are you using? What are you hoping to accomplish by extending maceration?
With Brunello the idea is to maximize tannin extraction. Tannin give the wine the ability to age for a long time. It also means that bulk aging will be at least two years and bottle aging another two before the wine is ready to drink. But another couple of years in the bottle may be necessary to smooth out the tannins and integrate the oak. When done correctly with good fruit the results can be stunning.