In principle, they are submitted by the carrier not the importer/exporter
So in terms of NI and Secretary's comments, the short answer is we don't know what this will look like - it will be discussed and agreed by the Joint Committee during the TP if the deal passes
However, countries like Norway and Switzerland have reached an agreement with the EU that allows them to wave that requirement when trading with the EU
So that could be one option for NI-GB trade. However, there is an alternative.