Prevent automatically reconnecting of Bluetooth devices

Hi there.

I have two iMacs side by side, a BT Trackpad, a BT keyboard, the magic mouse and a wired keyboard.

I'd like to use the wired keyboard and the trackpad on one iMac (let's call it No 1), the BT keyboard and the magic ouse with the other (#2) (both on Yosemite).

Whenever I shut down or restart the #1, the magic mouse connects automatically to #2. Even when I disconnect it on #2 and walk to the other and to see if it finds the MM, very often it has automatically reconnected to #2.

Is there a way to sustainable erase the Bluetooth entry for the MM at #2 (the retina iMac)?

Thanks for your efforts