No the trans fluid does not need to be changed when you do the driveshaft.
Unbolt the "old" driveshaft, replace all of the non serviceable u-joints and centering ball with greasable type.
Bolt the "new" driveshaft back in place, done.
Half a day.
It is recommended that you change your trans fluid every 30k and the filter every 60k.

After your "new" driveshaft is installed make sure it gets greased at EVERY oil change.
If you take it in somewhere they will not grease it unless you tell them to because every other DII out there that they work on does not have the grease fittings so they wont be looking for them.

They are called "sealed for life", but because they are so close to the exhaust and right under the a/c drains the grease gets baked and soaked, baked and soaked and then eventually the fail.
Good idea but bad design, you can thank BMW for that one as well as for not having a dipstick to check your trans fluid level.

Oh No!! the DII doesn't have a tranny check level????? WHAT!!!??

can someone in the Souther cali (los angeles/valley) recommend a shop that can do this, and possibly other work on my discovery (when I need it of course)?

Thanks,

Al

www.cartalk.com, find the "Mechanix Files" link, enter you zip code and recommended shops will come up.