We have ePO 4.5 and (i think) it's not possible
But it would be a nice feature for testing DATs ... pull the DATs to evaluation and test it on some machines ... if the test is ok, copy or move the DAT from evaluation to current.
You can manually change the branch from the Master repositories screen (change branch) , or schedule a separate "schedule pull" one for each branch at the times you want. Maybe a scheduled (change branch) task is a bad idea because you might have computers assigned to the evaluation branch and if the packages all of a sudden disappeared from the evaluation branch, they would have nowhere to get updates. ?my best guess?