If the UK leaves the EU it will almost certainly stay in the EEA, which means that (like Norway, for example) it will still be obliged to follow EU rules on things like packaging but without any right to help determine what those rules should actually be!
I do not know why either of those commercial issues would change.
In any case the sensible thing to do would be to agree bilateral trade agreements in order not to be manipulated by an existing power group that likes to dictate to all. If those agreements eventually led to a better fairer trade-only area, then that would be a bonus.