Can I register for VAT after January 1st 2018?

Yes, you can. Businesses registering for VAT will not face any registration penalty until April 30th 2018, but they are required to settle all the taxes due from January 1st 2018. Earlier, the deadline for VAT registration was December 4th 2017, which has been extended by the FTA to April 30th 2018. If your VAT registration fails due to incorrect documentation, you will be provided with a provisional TRN which will act as your TRN until you get a permanent one.