Kourtis,
The following is no way meant to be rude or negative. Since I am a PhD student trying to do something similar to what you’re trying to do, I’ll try to help you clarifying the openEHR space.
You’re looking for a complete EHR system with full functionality, which means it is a clinical system on top of EHR, that serves a particular clinical domain. On top of it, you seem to be looking for an EHR system build on a standard (it may not be). And you need it to be open source, and you also need it to be in a language you can easily modify.
This is going to be hard for you. First of all, Opereffa is not what you’re looking for, so I suggest you don’t lose time with it. Koray Atalag’s work may be closer to what you’re looking for: http://gastros.codeplex.com/ because it focuses on a clinical domain, but you have to evaluate it to see if it fits.
I also suggest that you look at open source clinical applications/epr/emr/ehr. Search terms may make a difference. You can also try to get in touch with vendors and ask for an internship etc, but it’ll be a tough sell, because you’ll ask for access to their code, and you’ll cost everybody time and resources, with little or no benefit offered back to the company. Plus, commercial vendors won’t always be happy about you publishing your findings. Still, give it a try, with so many vendors out there, one may find the idea interesting.
Given all these constraints, I suggest you consider working with a language you’re not familiar with, because that is the only aspect that you can control in the equation. Have you done your research about similar work? If someone else worked on a different aspect of your interest, such as moving an EHR system to cloud, you may attempt to improve on that by focusing on security etc. How about systems developed in academic institutions? Previous research is always surprisingly rich, in other words, as sad as it may be, we are usually introducing little to research even when we think we have grand ideas (that is my case at least), but this is how science works 
In short, the openEHR domain does not contain what you’re looking for, at least I have not heard about it. Maybe you may want to redirect your question to HL7 and 13606 groups too.
Kind regards
Seref