I am thinking that the following should be close to what you want:
a. Use dbSave to create a copy of the top layout
b. For each of the subcells, find the cellview bounding box, create an empty layout and create a prBoundary layout that has the size of the bBox
c. Replace each subcell with the empty layout using leReMasterInstances
Getting the pin part seems a bit difficult. Creating blackboxes with the correct pin layers and locations don't seem to be very straight-foreward.
>>>like to copy one or two metal net from top to bottom also is possible
Do you mean that you want to push the top level routing to a subcell?
Actually if your purpose is to do lvs verification on top level and treat all subcells as blackboxes, this can be easily done using the original layout. You can simply declare all the subcells as blackboxes in the lvs cmd file.
Would you please explain the purpose of creating such a layout?