It depends what format the codes you have are currently in.
If you know the protocol, device and command codes then you can use Makehex to create Pronto Hex strings.
If you already have Pronto Hex strings you can use the Universal Browser window in MX Editor/CCP and then press the Hex button and paste your code in. Then drag that code to a button on the remote.
If you want to do a bunch of buttons at once and have them available for future or repeated drag and drop then you can use "hexccf" to take the output from makehex and create a CCF file which can be imported using the Universal Browser window.
There are other tools that you can use for building codes and CCF files as well, but the above is probably the most straight-forward, albeit without any kind of GUI.
Current versions of these tools (and others) are available at [Link: hifi-remote.com]