freeze the reference DGN

Dear All,


                I have an problem to freeze the reference DGN.  I am working in project wise environment when I am going to create a new version of DGN files at that time attached references DGN are not freeze with old version DGN.

Means if any one update in references DGN so the attached reference DGN will update in old version of DGN as well in new version of DGN. Is it possible to freeze the reference DGN without merging the drawings.

Adeel Javaid