I would generally leave the load script to sort itself out because it's pretty good at doing that, the example you have identified above is one of the few times that I would force the load script to convert this to text, just because I wouldn't want to repeat the Num(EAN) expression every time I want to use it.
I have not used this before so you might want to check the syntax, but I think in the load script it would be something like:
LOAD Text(EAN) AS EAN_Ref
As I say, you might want to check the syntax of that one.....
Generally speaking, I try to get all of my values in the desired or most common format during the load. I like to do it explicitly in the script, but another approach is to go into settings, document properties, number tab, format it like you want it, and put a checkmark in "survive reload". Either way you do it, it's easier to format once than to format every time you need the value.