Somehow, when I ordered my Note 2 on Amazon, I managed to get into some sort of loop hole to where I got to keep my unlimited data on my 1st line (that I upgraded), rather than lose it to family shared... Not too sure how I did that?
Might be worth posting, just in case you can get away with it too.
At the time, I had suspended the 2nd line on my account (someone stole it) and had the S3 on my first line, which was eligible for an upgrade.
I ordered the Note 2, expecting to lose unlimited data, and activated it on my own by swapping in the old sim card. Then, un-suspended the 2nd line and put the S3 on it. Kept everything!

Might be worth posting, just in case you can get away with it too.
At the time, I had suspended the 2nd line on my account (someone stole it) and had the S3 on my first line, which was eligible for an upgrade.
I ordered the Note 2, expecting to lose unlimited data, and activated it on my own by swapping in the old sim card. Then, un-suspended the 2nd line and put the S3 on it. Kept everything!