There are several possibilities depending on your application. The Energy Management System (EMS) can be used in creative ways to alter the behavior of existing models, especially if they use Curve objects. The ExternalInterface (BCVTB) is available to co-simulate with an outside program that you develop. A collaborative developer license is available to get E+ source code so you can write your own fortran90 module and add it.
Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx
The primary EnergyPlus web site is found at:
The group web site is:
Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.