Can you change built-in parameters from Type to Instance based, and vice versa?  This post shows you can. 

The essence of the workflow is to

  • start a family with the desired template, 
  • add a value to the parameter, 
  • change the Family Category to something that doesn’t have that parameter built-in, 
  • switch the parameter to Instance, 
  • then change the Family Category back to the original

Read the more detailed version here:
http://aectechtalk.wordpress.com/2013/12/26/change-revit-voltage-parameter-from-type-to-instance/

(It is based on changing voltage parameter to Instance based for Electrical Equipment)