Standard datasource enhancement

Hello Experts,

I am new to sap bi....i have following questions.....pls help me out

1.I want to enhanced standard datasource (2LIS_11_VAHDR) for which i need to add few new fields.but the thing is datasource is already running in production?

2.I don't want to lose historical data & at the same time i need to add new fields?

So, pls guide me step by step enhancement procedure in above mentioned scenario.

Waiting for the earliest reply..

Thanks,

Satya