Yes, assuming the code that Binky posted works.
What you would do is download the
Special Protocols spreadsheet. Even though the Dreambox v5 remote isn't included, you should be able to use the protocol upgrade that Binky posted instead.
You can use this spreadsheet to format a Device Multiplexor upgrade that will let you switch which setup code is assigned to a device button.
If this is too hard to follow, do this; format the upgrade that you would like to be the "3rd device" and add it to your IR file. For testing purposes, assign the upgrade to a device button and verify that it works correctly. Then post a copy of the IR file for us.
When the Device Multiplexor is installed, you will need a couple of spare buttons to use as the new device buttons. For example, let's say that you have two different SAT boxes that you want to control, and you want to use the DREAM button for both of them.
Let's say that you want to use shift/rew and shift/fwd as the device selectors.
To control STB1, you would press DREAM, then shift/rew.
To control STB2, you would press DREAM, then shift/fwd.