I believe it is referring to the Change Document Indicator and not to make it editable in FB02 .
"The changes of the field contents in Transactions FB02 and FBD2 are logged in
change documents for SAP standard fields.
To activate writing of change
documents for customer-specific fields, set the indicator 'Change document' in
Transaction SE11 for the data elements of the fields and activate the data
elements .
As of Release 4.5A, this indicator is set automatically for fields that are
transferred to the coding block in light mode"
Regards
Ram