In my projects, I want to be able to modify the Duct Height, Duct Width, and Duct Radius parameters of the Duct/Fittings/Multi-Shape/Transitions, (see "Round to Rectangular Transition - Length.rfa" for this example) but for whatever reason these are set to read-only. Note that I do not want to modify any neighboring duct so that Revit automagically changes these parameters for me -- I want to modify the fitting's parameters directly.
To get them to be writable, I tried editing the family and setting the part type to something other than "Transition" (e.g. "Union") and then I could suddenly edit the parameters in the project. (Why is this? And, this won't work as a solution, since I can't modify all the system families this way.)
Investigating this further, I switched the part type back to "Transition" and then unlinked the Duct Height parameter from the rectangular connector. Now in the project the Duct Height was again no longer read-only. But again this isn't what I want -- parameter needs to be linked to the connector size to be useful.
So to summarize, there are two questions here -- 1) Why are these parameters read-only under this set of circumstances, and 2) Is there some solution that wouldn't require customizations to each of the families, e.g. maybe some setting at the project level that I could make to my project template?
