A lot of these questions are already explained in guide or in threads last few pages.
1. You want a serial and MLB that match your system definition. Although not strictly required yet, it's pretty clear on path apple is on it'll be next thing. If you are on an imac with a macbook pro serial and MLB, you'll probably be in next block wave.
2. You do not want a cloned ID for a mac you do not own, or one you do own that's currently still used with icloud or imessage. That's just asking for it.
3. It's probably not a good idea to use cloned info from a mac that couldn't possibly use 10.9+ or imessage. that's just me. Although it may work, it's a red flag in my book which makes it a good candidate for apple to target at a later time.
4. You need to ensure your serials are of proper syntax and actually match what apple expects. So no 3,1 mac pro definition with 17 char MLB. Use serials befitting of the definition used. if a 3,1 mac pro, a serial that you'd find on a 3,1 mac pro.
5. You need to ensure once your values are right that they are persistent before ever connecting to internet. DO NOT MESS WITH VALUES ONLINE. Clover is still better at this because filenvram from my experience, even when it's working, was always terrible at consistent values. It pretty much always generated it's own values at boot up anyways in any testing I did. This may be fixed in most recent version based on change-log I've been reading, but it's still inferior to the foolproofness of clover which lets you flat out hardcode ROM and MLB in RT variables.
6. Make sure your generated serial does not return as owned online. Last thing you want to do is look like idiot when you call apple and give them serial and they say "that's funny, this serial is registered to mr bob who's happily using imessage right now". There is a self warranty link you can use to check if a serial exists.
7. A damn good story when you call apple. Be prepared for questions that may put you on spot. They may say they can't find your serial and to verify it. I'm not going to give an example because I don't want apple to hear SAME story 100x either. With a bunch of us calling them, I don't want them to be alarmed. Be creative and confident. Don't sound nervous or stammer. Have stuff together before calling. This is actually one of reasons I like using older system definitions on purpose (provided you don't care much about power management or other things). less complicated MLB, easier to make up stories.
I personally haven't called back yet because it was probably 2 months ago when i called em last and they fixed me up. My lockout was from the mistake of having 17 char MLB where it should have been 13. I'm still waiting to see where apple ends up once dust settles and they finalize their changes.
