Wow, I know what's the differences between you and me.

For definition:
APN name: the 'ril.data.apn' field in current Settings, the value of APN field in the UI, and the 'apn' field of a apn setting in a single sim card of new Settings.

The implementation of mime is implemented based on:
1. User change the APN name, but all changes will become custom, this part is the same with yours.
2. If two settings with the same APN name, they will be merged into single one, and later one overwrites the former one.
3. As to no2, all the APN with the same name will be merged into single one. So, there should be no way to have   two APN settings with the same name.

All my knowledge about APN are from Ken. I think we should loop him in this thread again.