I've seen this question mentioned before and also on the Ubi forums. I even responded to them saying it didn't (when some others thought it did) as I installed the add-on numerous times on my computer. However, I got to thinking and I think I may be off in my assumption. With the DRM fiasco with Spore and Red Alert 3 I'm not so sure anymore. The reason I don't think I hit any snags was because my computer never changed between those installs. If I were to reinstall Windows or change hardware and then reinstall the add-on, will I eventually hit an install limit? I burned the add-on to a CD-R I had laying around. I even copied the add-on off the CD-R and reinstalled using that copy when I had to reinstall the game. I'm wondering if I actually need to get the Gold Edition of the game or not.
I did save the manual code that popped up when I bought the add-on months ago. Ever since installing that first time I have not had that pop-up appear in subsequent installs. I figure that if I reinstall Windows or something it may appear again and I can then use the manual code instead of needing to activate it online.