Can I update my Galaxy Nexus manually? I'm having a problem with music playback stutter on my Galaxy Nexus, and after searching about it for a while it seems the problem was fixed on update 4.0.4.

Unfortunately, my phone is still on 4.0.2 and no OTA Update is currently available.

From past experiences with my Milestone, updating or using a ROM that was not originally from my country (Brazil) resulted in various problems, including no 3G connection and very poor GPS signal.

Is it possible to actually update the Galaxy Nexus manually from 4.0.2 to 4.0.4? If yes, is there a way to know which "version" of the system would be compatible with mine?

Here's the "About Phone" tab on settings:
http://i.stack.imgur.com/0VZhk.png
AFAIK, the 4.0.4 is currently only available for the CDMA/LTE, but someone over at Modaco has a modified version of the 4.0.4 working for GSM.

It looks like everything is working on the GSM version with this modified release. I have also read that 4.0.5 will be released next month, so you may want to just wait.