Your concern is essentially answered in the various sections below:
I was struggling to come up with the right term, but decomposition kept rising to the top. I basically meant the overall decay that time affected as it went from Skyward Sword's era to Ocarina of Time/Majora's Mask, and so on—cellular deterioration, if you will. The skin of the Cursed Bokoblins became a brown shriveling rug that covered their bones, their faces became "wooden" masks, and the hair and horns fell off, although the eventual Redeads maintained their physical structure.
To me, this is where the emaciation comes in, although it I could be biologically wrong on this. I'm just thinking about becoming taller as they develop a scrawnier frame; not all things are tall and skinny necessarily, but Redeads are both of those. Another thing is that they're undead. Now, I'm prone to think that this means they're bodies aren't alive in any way which would also stymie cell growth), and that the evil magic is all that's keeping them mobile, but I also like surmising that the "curse" is not only what makes them move, but grow as well.
Both of these are things I can't validate, but I think the hypothetical curse justifies the explanation for them.
I don't know. Overall, I believe Nintendo has stuck pretty close to how the Redead/Zombokoblin designs correlate.
Wind Waker - Recall that these Redeads are found in coffins in this game. The enclosed space might have caused their bodies to not deteriorate or emaciate, but stay closer to the Bokoblin side of things. Contrary to OoT Redeads, WW's had a gray complexion instead of the original taupe, and they're almost more elephantine—just look at the ears—which tells me that they stuck to the Bokoblin side of things. Their predecessors could also have placed their undead bodies in coffins to ward off unwanted intruders in Dungeons and such.
Twilight Princess - And here the TP Redeads are wrapped in bandages. Now, this is later on down the timeline, so it's possible that the decomposition really begins at this point (as well as the curse's curative effects). They wear bandages so that their bodies don't deteriorate as quickly. That, or they were used to guard the prison known as Arbiter's Ground and were patched up as they lay dying from some huge revolt. I like to think the former suits this explanation better.
Really can't argue with that.
This is really just an attempt at branching this theory out a little more. Original hypotheses happen to be far-fetched a lot, but that's what makes seeking the end results seemingly worthwhile. Already more things came to mind because you prompted me to think about them better. In reality I'm not particularly good at theorizing—or rather, theorizing and backing it up sensibly. So thanks for putting up this challenge. x3
You have an interesting thought here, but if you look at it from that aspect, it isn't so much the undead creature in question evolving as it is the curse that created it, and the undead in turn changing because of the curse. While there is change going on there, that's not really what I'd call 'evolution', as deep down, they haven't changed from their original purpose at all. Of course, we'll never know for certain, but considering their body shapes, I can't really buy into them being alternate forms of the same creature. They may have similar faces, and similar functions, but that's about all they have. I do agree that they did stick to the same 'template' they did with the Redeads that they did with the Cursed Bokoblins.