Great questions. Several of these are enhancements planned for future releases of OBM. Current approach would be to use MicroStation tools to augment the final model from OBM.
For Creating specific custom Girders, try to use the section variation option available for prestressed girders as shown in screen shot below.
Have any of these design questions been addressed in new releases since the Nov 2017 posting? Such as the ability to add a horizontal offset/haunch to an abutment? In addition to the above items, I also wonder if any pier types other than multi-column or pile bent (such as a solid wall pier with crashwall) have been added to the templates.