I've searched but haven't found a clear answer.

Has anyone successfully replaced a 2-button keyfob remote with a 3-button model from ebay?

If so, how did you do it?

For a 1999 B5, do I have to worry about this immobilizer chip I'm reading about? Some say yes, and others say that 1999 and prior models don't have the immobilizer chip.

I don't care to make the 3rd button do anything. I just want lock and unlock to work.

If I could find a "like new" 2-button remote, I'd be fine with that, but I can't. 3-button remotes are everywhere on ebay.

 

Hey i had some issues with my switchblade too when i first purchased my car. But i got my remote to work. In your situation with the 99 b5 do you have a current switchblade key head unit, because you can then just get the bottom part with the button which if you look on google you can find a few sites.
http://www.ikeyless.com/audi/a4/1999..._trunk_release
if you look harder i know i have seen a few refurb switchblades for cheap. as for going with a three button i dont know if that would work.