control angle of sloping beams

If you mean, is there an option set to change the default use the first rather than the second method described in that book, no. There are many different sources of information about beams and other engraving details, most yielding conflciting information. We tend to default to trying to adhere to Elaine Gould's "Behind Bars" as the current definitive work, and she based much of what she writes on this subject Ted Ross' "The Art of Music Engraving", which is absolutely the msot authoritative work ever on this particular subject. And while Gould mentions that some editor go out of their way to avoid the staff lines, she does not recommend this practice. I check actual published literature, I don't really see many editors going out of their way to do that, either.

Anyhow, the beaming code is incredibly complex right now - probably the most convoluted part of the entire program. So I would say adding further options to control this is possibly, but very likely none will have the stomach for it, as it is involves messing with very delicate code, and it seems to me this particular preference is non-standard. So most likely, you will continue to need to do these adjustments manually if you really prefer it, at least for the foreseeable future, unless someone steps it to volunteer to try to implement an option.

The "Shorten stems" options, BTW, have to do with notes utside the staff but with stems pointing away from the staff and the degree to which they are shortened from the default 3.5sp.

I see this post is from several years ago. I wonder if there has been any update on that since. I also find that the slope by default is always a tad too steep, and I wonder if this default can now be modified in any way.