Perhaps you could customize your tags by using a semicolon instead of a comma in the tag body.
As for "could be modified", perhaps so -- see what Kovid thinks.
I don't believe anyone has ever requested it before, which explains why it definitely wasn't an option thus far.
Personally, I think library science should change
the primary purpose of a tag is to help people find things, and relational databases allow you to find things a lot more easily than the flat card catalog model.
I see no reason to limit yourself to the old ways. Break up your tags into a form more easily manipulated by queries.