The copy command was added to hexed a little while ago. This command has 2 modes of operation: copy (c) or copy overwrite (co).
The Command List
Copies data from the source inserting it at the destination
-c 100 200 20
This will copy 32 bytes from 0x100 to 0x200 moving everything at 0x200 up by 32 bytes.
Copy Overwrite: -co
Copies data from the source overwriting the destination
-co 100 200 20
Copy 32 bytes from 0x100 to 0x200 overwriting the original data.