I finally got it working after a friend/colleague at work gaved me his macbookpro id's since he works as a DJ and never uses any single apple services.
I only used his MLB and ROM and generated my Serial Number & UUID and it worked on first try.
Every ROM value I got so far is completely different. There is nothing in common, except all OUI values belongs to Apple. I have no idea is OUI depends on model, production place or something else.
What are first 3 chars of MLB that you got? C02, C07, C1M or some other?
What is OUI (first 6 chars) of ROM you got? Is it any of those: 7c6df8, 406c8f, or something else? Maybe one of those from this list?
http://www.adminsub.net/mac-address-finder/apple
When you tried to change a value, which value did you changed? Do not try to change first 6 chars of ROM (since you will break vendor information), change just last two for example. Just be sure that you using only hex values (00-FF). For MLB you can try to change last two chars to any of those (those are some of valid values for last two chars of MLB): '1H', '1M', 'AD', '1F', 'A8', 'UE', 'JA', 'JC', '8C', 'CB', 'FB', 'A6', 'AL', 'AN', '16', 'A5', 'AH', 'AA', 'AD', 'AK', 'AN', '1W', 'AY', '1A'.
EDIT:
Looks like MLB and ROM are actually registered as a pair, or at least some calculated value based on those two values. Valid MLB and valid ROM that are not registered as a pair doesn't work. I replaced last two chars of MLB and last two chars of ROM with values from other MLB/ROM pair and that doesn't work, even both new values are in valid format. It might be possible to call Apple with a code, and that this will work after registration on their servers as a valid MLB/ROM pair.
I can't be sure, but it is possible that calling Apple with support codes doesn't work if MLB and ROM values are not in valid format. If LAN MAC is used as ROM value (as instructed), that value will have OUI of your LAN card manufacturer. For example I have a Dell laptop and my LAN MAC address starts with 20:47:47, witch is OUI that clearly stats that LAN card is made by Dell.
If someone wants to try to call support and register new unique combination of valid MLB/ROM pair, please send me PM, and I will generate some new, generic (but still valid) values for you.