How do you best modify an existing piece of equipment?

edit

An answer to a similar question can be found here. Basically, you can edit the hvac_library.osm file manually to include the collection of objects you need (see the linked answer by @aparker to yet another related question), or use the OpenStudio API to write Ruby code to add objects to the library (@Kyle Benne's answer), which is not exactly a measure, but close.