To make a fake ID you need to hack the habitat's database AND comms section (the one that allows communications between habitats). You then add yourself with the data you want, and associate it to the nanotat ID in your morph, brain waves, etc... The hacking of the comms system would just make all requests to automated sources of data about you to other habitats to show what you want as a response (and send you a copy of the requested data, so you can be alert someone is sniffing around you). You could even make it go talk to a fork of yourself disguised as someone of other habitat, or if there is enough time dilation, you could forge a video response. Illegal morphs could be ones that do not abide to local regulations (like a Reaper in a pacifist habitat or whatever), and to get them you need to contact crime sindicates. Unsavory backgrounds doesn't mean automatically criminals or something like that, in the first Takeshi Kovacs book he was sleeved in the body of a cop, and that gave him automatically some advantages (the cop's girl wanted the body intact for her boyfriend, for example, and she had pull) and disadvantages (there were criminals who owned the cop some payback). In EP that is a little... more complicated, thanks to AR. Let's just say that the "unsavory backgrond" might mean that a criminal cartel uses that body for their hitmen...