So screed can change a black miss into a hit crit. Can he change a red miss into a double hit?

Nope, just to a crit face.

Also, not sure if you know, but there is a rules sub-forum for rules questions like this. Not that I think anyone would give you grief for posting on the main forum, but you'll likely get better answers over there.

since Screed's card specifically reads a crit face, as Ardaedhel said, the answer is no. However, abilities that allow you to change dice to a face with a hit symbol (such as Warlord) can change to a double hit. Alternatively, effects that require you to spend dice with a hit symbol (such as Precision Strike) can be used on dice that show a hit, a hit-crit (on blacks), or a double hit (on reds)

Nope, just to a crit face.

Also, not sure if you know, but there is a rules sub-forum for rules questions like this. Not that I think anyone would give you grief for posting on the main forum, but you'll likely get better answers over there.

Doh! Thought I was. That'll teach me to post from my phone.