SEP 12.1.2: Adding package from one SEPM to another?

Hey Guys,

We're trying to move clients from 1 sepm server to another and our idea is to make a package where the sep clients should be reporting and add this package on the old sepm server and put it on the Installed package of the group we are moving, so when the heartbeat of the package happens it will install the new package to the clients on the group and move the clients to the new SEPM. BUT WE CAN'T PUT TWO SIMILAR VERSION AND  BIT PACKAGE, how can we do that?

What we need to know:

1. How to add another package on the SEPM if it is already existing? when we try to add it says "package already exists"

Thanks,