The 2019 National Banger Rules have been published and can be accessed through the link below. http://www.stockcar-racing.co.uk/_assets/documents/rules/2019%20National%20Bangers%20Rules%20-%20Issue%204%20as%202019-01-18%20-%20Designed%20For%20Printing.pdf
As it says at the end of these rules, they come into effect from 1 February 2019.
This means that the Unlimited Banger Icebreaker will be run to the 2018 National Banger rules, but the 1500cc Banger Icebreaker will be run to the 2019 National Banger Rules.