So the last time I spoke to the chaps from Comand Online in Lightwater they said Mercedes were not allowing Distronic Plus to be added to the datacard but regular Distronic was fine.I recently retrofitted all the distronic hardware to my 2003 W211. All went well until we went to get it activated by STARs only for Mercedes UK and Germany to say they wont allow anymore vehicles to be retrofitted with the devices that it didn't come with from the factory. So just a heads up for you too unless you know a different way of getting it to work or if its simpler on C216 era of models
I am not sure exactly how it fits together on the W211 but it is possible on the 216 and 221 to enable it without the dealer or adding it to the data card. A caveat is if you ever have any programming done it will need re-enabling but using Developer mode on STAR (DAS specifically) or Vediamo is how you can still enable it manually.
I suspect you could still enable yours.