Response from Shure
I wasn't expecting a response from Shure so quickly (or at this hour).
So, I had sent an email to Shure as well, but was under the impression I would get a response somewhat like, "We cannot comment or advise you to do so." However, I did not get that response.
In case anyone else was curious, the answer to my question is "Yes."
With the Beta 57A and 58A, the grilles are interchangeable and changing grilles achieves the result of the other. Good to know! =)
Looks like in the future I will just buy a handful of Beta 57A's and a couple 58A grilles for those just-in-case situations.