1st you have to see if the lili belle is out, then i believe you can ask the conductor to ride. (please correct me if I am wrong)
for something extra special you can make reservations at your favorite place to eat, pleanty to choose from in Dl DCA and DTD.
You can also get a birthday button from City Hall when you arrive, and a set of ears with a crown or party hat.
See the shows try to participate for extra special memories.
I know someone out there must have better ideas than mine ....
Disneylandfan95 is right but Id like to add that you might not go right away. From what I understand its if they have enough staff available too. So lets say that the lilly Belle is out on your B-day GREAT As a CM and you probably will be able to, I dont see why not, but it might not be till shift change at 3 or 4pm, because they might not have enough staff on in the AM to accommodate you. I'm pretty sure you have to do the whole tour of DL not get on at Main St and go to Toontown lets say
on our trip we were told that we had to go to city hall 1st thing in the morning and book a reservation for the lillie belle, if it was available that day.. that was from one of the conductors there on main street.
Definitely go to City Hall first and get yourself a birthday pin (and you can ask about the Lilly Belle there too...never hurts to cover all bases). You will have cast members saying "happy birthday" to you all day long...it's really nice.
Lilly Belle only gives out 3 rides per day (if that) and you need to get over to the station early in the morning to get put on the list for an afternoon ride. Tell them its your birthday, they really try to accomodate special occasions but it is never a guarantee due to staff requirements. Good luck its fun.