to get some insight, currently the most informative thread is http://www.cruisersforum.com/forums/...lay-41640.html
Basically you just have to edit the files in s57data, but for some object which use more complicated logic, modifications to the source code are needed.
You can find the rules editor at OpenCPN - Rasterization Rules Editor - Redmine
and the most recent development version of the rasterization rules at nohal's RleData at master - GitHub
If you have any questions or need more information, contact me (if you prefer e-mail, my address is on the authors tab of OpenCPN About box)