You won't be able to have more than one McAfee Agent on each branch.
But you can perhaps try this:
- Download and check MA 4.5p1 into the previous branch
- Create and download MA 4.5p1 installation package
- Check again MA 4.0 into the previous branch
Now you have changed nothing in your repository but you have a MA4.5p1 to be installed on the machines you want to make the test.
Also, depending on how widely you test - you can manually install Patch 1 over an existing agent using the framepkgupd.exe package, which will upgrade the agent in place, preserving the ePO server details - so you can have patch 1 in place without having to check it into the repository.
Obviously this is a bit impractical if you're going to be testing on a large number of machines, though.