I'm confused - you need to buy a deer tag if they'll still even let you. It's separate from an elk tag. What "difference" are you referring to?
If you're referring to your hunting LICENSE then, no, you don't need to buy another one of those - just the tag.
If you're referring to buying a deer and elk license separately as opposed to the big game combo, you'll have to pay full price for the tag not "upgrade" to the combo license.
Not sure if I answered your question because I'm not sure of your question.
Anyway, sometimes posts can come across harsher than they're intended and I don't want you to think that I'm treating you poorly - that's not my intention. Please just clarify the question.