Thank you very much for your reply.
I've done exactly as you have commented, installing Impulse in a computer with Internet access, and registering GalCiv2UE using the serial number included in the box manual (BTW: Impulse has failed and closed twice. I've sent a report to Stardock, reference number: 801216). Then I've accessed to Impulse Anywhere from Firefox, using the same account and I've seen there GalCiv2UE, and the possibility for download a full offline and updated installable copy (version 2.03.007).
That's the nice part.
Now the ugly one: I'm downloading those files but it's going too slow, at about 80KB/s (and the total download is about 2GB in size!!), so it will be a task for some hours. Moreover, some parts are failing time to time (luckily, the download is not an enormous lonely file, but eight parts), because they can't be read from the server according to the firefox error message.
But, in spite of being an uncomfortable and disproportionate process for a simple update, that's better than nothing I suppose 
I'll post again when I'll be able to install GC2UE in the offline computer (surely this weekend), if I find any kind of problems with unlocking and activatig this Impulse 2GB self-extract thing.
Thanks again.
Edit PS/ As a suggestion, please add MD5 checksums to those big files to ensure at that very moment if they've been correctly downloaded. Thanks.