>>You may be better served having users define data validation constraints
I do use that. It helps with keeping the data correct, but has no effect on how the data acts when exported. In Excel, you can type '1 to mean "the string 1" but then you can turn around and put a plain 1 in the same cell, and all will be fine. So I think I can only do this with a meta-Excel option, where the user specifies a genuine data type. Fortunately, it'll only be necessary for oddball situations like this (large numeric IDs, and maybe a few others I haven't encountered yet). Thanks, all!
