If you want to only copy jobs from one specific client from an existing copy you can follow these steps:
create a new synchronous copy
Under the associations tab "uncheck" client and computers
Check off only the client/subclients you want to copy
On the copy policy tab you can setup the criteria as for date/source copy
Once you have that entered - finish by selecting a name for your copy, target media agent and library - then you should be good to go.
You can verify jobs that will be copied to your new policy by "viewing jobs" on that copy as they should show to be in a "to be copied" state.
After you have verified all the jobs for that client are prepped to be copied - right click on the storage policy and run an auxiliary backup for your new copy.
Note - You may want to combine streams to a single datapipe for writing to only one tape.
(If you only want full backups - follow the same steps but instead use "selective" versus "synchronous")