No, it is quite simple, but there is just a problem to solve.
The proposed CSS in the current version is "dinamic". This means that some values in the CSS can change depending of the user choice ( font dimension and font face)
I can easily allow to choose an alternative CSS but this will be "static" and you cannot anymore change that parameters by preference window.
To enable parameter change even in external CSS I have to rewrite a lot of code.
Let me know if the first option is enought for you.
I don't know anything about programming in openOffice.