If you search the forums for “serial-direct” you will find this is a very common approach to hook up an emonTx to a Pi, depending on how many 3ph CT’s you require and how accurate you need the “real power” to be, you may even want to consider 3 emonTx’s, this has also been done many times, usually by connecting all 3 emonTx’s via USB serial adapters, but since you are using a Pi B, you could have one connected via the conventional “serial-direct” route of using the Pi’s GPIO serial port and 2 more connected to the 2 USB ports (if you are using Ethernet and not a wifi dongle).
There is no “transformation” of the code required, just a few configuration settings.
Depending on whether you go for 1 or 3 emonTx’s you may need to upload a different sketch or tweak some settings, but no real coding should be needed.