Does Excel care what you put in a cell? Does it object when you get a resultset from SQL server that is different than before?

Yes, it actually does care. As a matter of fact, it might object, depending on the nature of the change. Excel might generate an error, or the Excel content (pivot table/pivot chart) might "blank out".

Because of this, sheets that use pivot tables bound to OLAP cubes or database views will sometimes have macros to self-refresh, because of back-end changes. So, just like many things, "it depends"