You can use Copy to New Revision 
to create a new variant or revision for the BOM. BOM attribute data is copied to a new revision or variant without copying the BOM items.
To copy a BOM and create a revision
1.Select the BOM you wish to copy from the drop-list located in the upper right part of the screen.
Copy BOM Button
2.Select the Copy BOM button and option for the copy.
If you select New Revision, the BOM form will appear with all fields copied except for Revision and Variant. If you want to copy to a new Variant, the variant will be the only field that needs to be filled in.
Revision and Variant Fields
After the copy is done, the BOM revision or variant is ready for import.