Ideally if the MWPL is hit, NSE bans the F&O contracts and the brokerage where you trade will block taking new trades in the F&O contracts, you are allowed to exit existing positions. But there is no restriction on trading the actual stock/equity.
You will be able to trade only once it is off the ban list. You will be able to see the exchange messages on your terminal which will show when any F&O is put on ban or removed from it. Also check this: http://tradingqna.com/3391/stock-futures-under-secondly-short-scrip-will-happen-incase