No problems changing the schedule from 12-6 to 9-9.
I don't really have much thoughts on the 12/12 vs. 11/13 except that personally, I've always used 12/12 in flower (even when using the GLR in veg!) and, theoretically, the more light the better, so I would never argue with or fault anyone for using 11/13. I don't know if that helps at all, though!
EDIT: I'm assuming we're both really talking about 13/11 with 13 hours of light and 11 hours of dark! I believe you should list the number of hours of light first.
I don't really have much thoughts on the 12/12 vs. 11/13 except that personally, I've always used 12/12 in flower (even when using the GLR in veg!) and, theoretically, the more light the better, so I would never argue with or fault anyone for using 11/13. I don't know if that helps at all, though!
EDIT: I'm assuming we're both really talking about 13/11 with 13 hours of light and 11 hours of dark! I believe you should list the number of hours of light first.