Why is it that you're not comfortable with changing XLAM? Because of issues like this? I've changed the XLAM directly for years now, and until now I've never regretted it.

Addition: There's one problem which repeatedly bit me, and which may not occur when working with XLSM: It has no “dirty” flag, which means if you don't explicitly save it, your changes will be lost.
You just answered your own question