Hi Deepak,
You are correct.
I recommend to create new Non leading ledger which will applicable from 2013 on wards.
For new non leading ledger doesn't have any data in FLEX table,however you just created new non leading ledger.
If you want entire previous posted data with proper fiscal year variant wrt new non leading ledger,you must transfer data from BSEG to New non leading ledger ( In selection itself having option where to move) with using of above suggested process.
Try for one entry and check impact. I did for 5 years data without any issues.
Regards
Mani Kumar