Your question reminds me of the wish to be able to freeze the area of a fill but still be able to graphically change its shape.
This would be even better if available also for zones.
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"