I suggest it as an alternative approach. It's live in that at any time you can rebuild from model. You would still have to delete the non-window lines. You might even apply the new penset to this elevation. It could be easier to edit out the little bits that you still have trouble with.
Another thought is to place a masking fill to cover up all but the window.
Without seeing what specifically you are working on, it's hard to know what might work best. I'm just throwing out some alternatives.
HTH
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"