Brit living in USA wanting to move (back) to Norway

Hi,

I am a Brit currently living in the USA. I lived and worked in Norway from 2010 to 2016. I would like to move back there sometime in the very near future with my husband (he's American). Because of the whole Brexit thing, I've read that I'd need to re-register by the end of 2021.
First of all I wonder if I can even do that if I haven't lived in the country for 5 years, and have no ties there. And secondly, if I am able to, how would I go about doing it? Do I have to be living there to do it, or could it just be done on a long trip there, for example?

Thank you in advance!