lewm,
"Please define factory settings for SME. " The ones I have worked with have a string and weight arrangement and a scale with markings. Set the string on the Antiskate scale to correspond with the VTF.
"For Technics, how would one determine 50% of recommended settings?" They have a dial with numbers which correspond with VTF in grams. So, for example, if you set VTF at 2 grams, Technics recommends that you set the dial at 2. I am finding that number high and suggest setting it at 1. At least to start. Admittedly I haven't tried every cartridge and there is variation, so this is a starting point.
"And what about the many well loved vintage and even modern tonearms that still use a string and weight or a rigid lever and weight (e.g., my Kenwood, Dynavector, Triplanar, and Reed tonearms) to set AS? There are no settings, as such."
I have not set up a Triplanar since obtaining AnalogMagik. In light if my earlier experience with at least 2 different versions, although I find them to be a challenge to work with, they are exceptional sounding arms and I would be surprised if following their recommendations would be anything but accurate. Kenwood, it has been almost 20 years since I last played with one, but again a wonderful TT. But I am out of date. Zero experience with Reed or Dynavector. Given their reputation, if I were to address one, I would be inclined to set it up in accordance with the manufacturer's recommendations and give it a listen. If I hear anything tizzy, a technical term I am sure you are familiar with, back off AS a smidge and listen again.
Generally, it seems as though the AS force imposed on a lot of TTs is higher than needed. It is a problem. Another problem, a much bigger one believe me, is the dirty stylus syndrome. It never ceases to amaze me that a guy will want me to check his stylus for wear and before I can begin we have an excavation project to uncover the diamond, buried as it is under so much debris. Very often this stuff is very encrusted and resistant to removal. I am not telling you about $50-$100 cartridges either, no Atlas and Anna and like that.