Please Help: GST opting RCM to FCM by GTA

Sir, i have a query, there is a Transporter who is Presentaly Raising Invoices 5% without ITC, Now he has purchased some Capital Goods they have huge amount of ITC so He wants to go for 12% with ITC,

My Query
1. he can go for 12%.????
2. if Yes, When He has claimed all ITC, whether he can opt again 5% GST without ITC