Well you see, it doesn't matter if I change the year for one disc or keep it the same for both. If the album is 2 discs, it's going to play in order, disc 1 then disc 2, on both the phone/mp3 player and MusicBee. Sometimes I just want to listen to the original album, other times I want to hear some live tracks off the bonus disc. It's easy on the computer because I can just queue the songs I want quickly. On a phone it's not as simple to do that...
I guess if I want to keep my library organized and not have an album split up and titled "Disc 1" and "Disc 2" at the end of that album's name, I will combine them into one disc and give the bonus disc a separate year. I will use grouping field to note that it is a bonus/live disc.