On the issue of green-slips as proffers - If you put in for a green-slip you are "requesting to fly" and are expected to be available. You can use the GS filters or just put in a blanket GS and screen your calls - both methods work.
In a perfect world if you are going to be 'out of position' you should not have a green-slip in the system. Or as has been said before don't answer the phone.
I have turned down GS's before and never had a scheduler ever say anything other than OK, and smartly move on. I'm sure if they are desperate and you are the third pilot with a GS in that couldn't take the trip they would naturally get a little frustrated and understandably so.
Scoop