Judging by the look of his saddles he appears to be a BCI of some sorts, it doesn't appear that he's a morph of any kind. His shortened tail could be the result of several things, but yes REALLY poor sheds can result in shortened tails. Live feeder rats also have the tendency to target boa tails if left in the same enclosure for an extended period of time. I'm not saying that's what happened, but I've seen it before on these forums.
As for the skin, it appears like he's close to shed in the pictures you just took as he's going opaque. What I like to do before my boas go into shed is to just place them in a lukewarm shallow bathtub and just let them sit for 20-30 minutes. It helps with the shed process as boas are not known to soak by themselves typically. Be aware however, this also usually causes them to defecate.
It's hard to say what you're talking about concerning his belly skin, but I'll tell you that judging by his appearance, he appears to be much older than just a few years. He doesn't appear to be skinny or underfed by the photos you provided. Wait for him to shed, then post a few more pictures of him. I'm not seeing anything out of the ordinary about his appearance as far as his skin is concerned however.
As for handling an agressive boa....it completely depends on the individual animal. Many boas are prone to "defensive" strikes only, meaning that if you can find a way to pick him up he SHOULD settle down, but you also need to be very aware of his head location at all times. They are an animal that REALLY like their enclosure and sometimes they do not like people messing with their habitat. Almost every one of them calms down once you get them out of the cage however. Just be careful.
Boa care is rather easy to remember however (these are the temps I maintain my animals at)
80 F cool side
90 F warm side
50% humidity.....ideally bumped up to 60% around shed time.
Edit: This is why BCR is a mod, gets here fast and summarizes everything I just said in a hell of a lot shorter terms lol.
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