Sorry, we don't have much documentation public yet and it is not possible to change the content processor logic for each user yet either. But if you want to beta test it, you can get in touch with me and we can give you instructions how to do that. Basically you just need to derive from an interface called IContentProcessor, which has one method: Process. Next you can define a dynamic script for each incoming content file and platform, which is run for every conversion.

Other than the basic idea to have content processors there is nothing like in XNA. In the past we tried out local content processing and putting it all into Visual Studio, but that did not really work out well. So in SoulCraft we used custom tools to do this only once on one machine and in v0.9.0 we have improved that by doing everything in the cloud (but disabled most content formats since we are not done yet).

To get you started you could just write a simple test or console app that reads your TEF file and outputs a binary file (should be easy enough ^^).