I have an autumn farm scene with the sky visible through a multitude of openings across a tree line and will be either changing the color in the sky or bringing in from another image. What technique would you suggest to efficiently affect a similar change through the tree line?
You will find tutorials for this by googling for (masking trees in Photoshop):
How easy or hard it will be depends on how similar the sky is amongst all the openings in the trees and how dissimilar it is to other areas of the photo. In other words it might be a few clicks of a magic wand or similar selection tool with Continuous turned off, or it might be very painstaking.