How do I format text to appear with a space after each four characters, as in abcd efgh ijkl mnop (etc). Or with mixed alpha-numerics AB12 3456 CD78?
There is no format code available to change representation of text (apart from ability to prepend/append some static text; see “Text and Text” there).
So if you want that, you’d need some formula cell that would actually change the string - like this formula using new REGEX function from version 6.2:
=REGEX(A1;"....(?!$)";"$0 ";"g")