You can do anything you want, is it smart? No.
12 weeks on Anavar is a long time already, I would not recommend that in the first place. I would shorten Anavar to 6-8 weeks and I would not add SD to another oral either. Either run Anavar or SD by itself or you can get an Anavar Winny combo (they are usually 25/25mg tabs) if you want to double up on orals. SD is harsh on its own.