I've found using generated fake serials are not reliable eg if you clean install OSX on a different hard drive (even using the same Clover config.plist in the same machine) or logout of iMessage on an OSX install with iMessage previously working, then you can often get problems logging in again - the "contact Apple" message usually requires a genuine Mac or iDevice to reset your AppleID password when things go wrong.
Using genuine serials, I can login & logout and install OSX on multiple partitions and iMessage still works (even without credit card attached to my AppleID ). I have written some background on the iMessage problem in my post in the Clover General Discussion thread. I have replicated my results on my 2 hacks
Dell XPS m1530 Laptop using genuine serials from MacBookPro 2011
Desktop GAP55aUD3/i5-750/Radeon5770 using genuine serials from mac mini 2012
With genuine System Serial, SmUUID/Hardware ID, MLB and ROM ---> works 100% all the time, even without credit card.
From @heryts testing, you must have at least MLB & ROM from a genuine Mac or validated Hackintosh (where you have called Apple Support).