You have a requirement to change the Properties of a particular field whereas the Field is missing in the Adaptation Mode.
SAP Business ByDesign
The reason that you are not able to view the fields in the adaptation mode is that these fields are extension fields which have been added via PDI and therefore these fields will not be available in the adaptation mode.
Any change to the PDI fields should be performed by the User who created them in the respective tools. User extensions can be edited in Business ByDesign itself in respective screen.
PDI Fields, adaptation mode , KBA , SRD-MD-PRD-PRD , Product , How To