[oXygen-sdk] Overwriting or Extending the DITA framework

Hi, We are creating a plugin for oXygen (14.1) for our DITA based repository. We have some customizations (not specializations) on the DITA DTD's, but our DITA files contain the standard DITA public id's. Is there a way to extend the oXygen DITA framework, so we can 'inject' our catalog instead of the default DITA catalog? These customizations also require special rendering in the Author view, so we also need to extend the standard DITA css files. We can make the distinction between standard DITA and DITA files coming from our repository, so we would like to do this without changing the default behavior of DITA files not coming from our repository Kind regards, Pascal