When you say you can't find anyone at DLR to answer your question, I'm curious who you called. Your first question is very simple. It's even answered in the FAQs on Disneyland's web site.
"Q: Can I upgrade my free admission?
A: Yes, you can be upgraded to a ticket type of equal or greater value. However, you are responsible for any additional cost, and the new ticket may be used only by you."
As for your second question, I had not heard the 2fer ticket is being given as the birthday admission, but if this is true, you can upgrade tickets as long as they are still valid. So... that would be up through the use of the 2nd park in the case of a 2fer.
- Dreams
I called DLR the other day to get confirmation about the 2fer (which I had read on this thread) and I specifically asked about the upgrade. The first person I asked said "oh, I'm not sure, let me transfer you", and then the second person "the last info I have said, no, not for hoppers unless you add days", but she put me on hold to find out for sure and never came back to it.