Dear Amit,
You Can track the changes in BOM through CC03 OR CC33 In SAP
Procedure is:
1) Make ECN by CC31
2) Approve or Release it by CC32
3) Make Changes in BOM by CS02 or Mass changes CS20 against ECN
4) Release ECN again through CC32
Track the Changes through CC33 OR CC03
BR
Madhukar Poul