Muse Patterns are indeed designed for a 5' 10" woman. There are quite a lot of tall women who sew - in fact, for tall women it's often their height that got them into sewing in the first place, due to frustration over RTW garments that are too short in the leg and arm, and don't fit across shoulders! And yet, very very few patterns cater to this demographic, so we all have to make changes to every single pattern we buy. I'm tall myself, so to me it made sense to design patterns for people who are in that demographic. :-)
With the adjustments - for people shorter than 5' 10", there are really only two areas that you may need to adjust with the Jenna pattern. The sleeves will almost certainly need to be shortened - they're designed to go down past the wrist on a tall women, and are very likely to be too long on others. This is a super easy adjustment to make - simply fold some of the length out of the sleeve around half-way down the pattern piece, smooth out the line of the side seams, and you're done! :-)
The other area of adjustment, which you noticed, is at the shoulders. Depending on your individual build, you may or may not need to adjust these. Since Jenna is a knit pattern, a good way to check is to measure the distance across your shoulder and compare to the pattern piece. If you need to take any width out, you can fold it out from the middle of the shoulder and smooth out the line.
Aside from those two alterations though, there shouldn't be any others needed as a result of height differences. For more fitted/woven garments with waist seams there may be due to different torso lengths, but for this style that should be all you need, and they're nice and fast to do.
Hope that helps!