How to make Cost Centre as an Editable Field for Specific Approver level in Schema

Hello All,

I am new to SRM and BRF. I have used the standard Workflow for shopping cart Approval.I have used BRF(Schema Levels) to determine Agents.

Now i am facing two Problem and seeking your help:-

1) I have to make COST CENTRE as editable field so i checked in SCN and found that i have to tick the EDITABLE checkbox in /SAPSRM/V_MDF_IC but i couldnot found COST CENTRE field here.There are many other fields which are at line items but couldn't found Cost Centre.

When i tried to make a new entry it gives an error that COST CENTRE does not exist in some structure.

2) I have also inherited the Standard Class /SAPSRM/CL_PDO_DYN_MDF_WRKFLOW to a Zclass,But here we only want to have COST CENTRE in EDIT mode for First Level of Approver Not for other levels.So here i put a break point and checked, but i am not able to get how to distinguish if it for the

First Level of Approver or some other Level for the same Shopping cart.

Please help, points will be rewarded.