I did, it worked fine. Note though that you have to install the Agent 4.6 extensions, which will overwrite the 4.5 extensions (they are backward compatible). Also, I didn't try installing more 4.5 agents after I had 4.6 in the evaluation branch. The existing 4.5 agents continued to work fine.
There's a setting somewhere in the ePO configuration screens to allow checking a package into any branch that has to be enabled.
Yes, you can definitely do this.
Make sure that ability to check in the package to other branches are enabled from the ePO server (Menu=>Configuration=>server settings=>respository packages=>Edit. Select yes 'Allow package check in for any repository branches'.
Thanks for all you guys responses. I am currently testing this out on my non-production ePO 4.6 server.