you can't really negotiate trade tariffs without agreeing on consistent regulation (i.e. you won't be able to sell stuff which is illegal in the EU). So basically you end up in the same position, having to abide by EU regulation, but without having weight in the decisional process. It's silly, really.

FWIW, there is a host of things where nothing will change, as most treaties don't get invalidated and the UK is still a member of the council of europe, EEA, EU customs union etc