0) I've started watching this topic (and may add others) as I have a Thomann AK-X1100 (Medeli AKX10 with less storage) on order. - I have no experience (that I can remember) editing PSR-styles, but I have edited Band-in-a-Box (BiaB) styles. (No, these are quite different, and their file format is a trade secret.)
1) A piece of software that can at least read and write PSR-styles (and maybe read BiaB styles; I haven't checked for some 15 years) is
Harmony Assistant (macOS, Windows, Linux). It's software that uses music notation, so it may be "at home" for some and "oops!" for others. If I remember correctly, style files are on a special staff, all patterns in a row. - There is other software that at least can use PSR-styles, like by
Jos Maas. You may want to visit his site even for resources.
2) Back ten, I was a member of the Yahoo Group on PSR-styles. I seem to remember that it was all but dead when Yahoo terminated the Groups. The group (like every Yahoo Group) had a file repository. I remember that some styles were way more elaborate than others. - Like everywhere else, everybody wanted all the good stuff for free, and contributed nothing. - I can tell from experience, how much effort can go into crafting a style. (I spent some time creating a simple BiaB-style in csardas (czardas) fashion (slow-medium-fast): just Upright Bass bowed and plucked and Bratsch ("viola for chords", so I used the Viola instrument), yet got tired.
3) I have used BiaB from 1995 to 2005 (but I have sometimes updated). I used to be reluctant to change styles. My work-around was: substituting the instruments in my song files. Like even selecting Rhythm instruments for a Pad part, and reversely. Or just muting unwanted parts. I remember adapting some Country style for (the middle part of) csardas by replacing the plucked Upright Bass with a bowed one, replacing the Banjo with a Dulcimer (or similar), and (I think) the Guitar with the Viola. I would play the melody (Violin) live on a wind controller (Yamaha WX5 and VL70-m). - Substitution by instruments of another nature may be a simple way of making a style work for you.
Sidebar:
4) I have a wide scope of music (in place and time), and I still consider the Hungarian accompaniment of Upright Bass, Bratsch and maybe Contra (Kontra? - a plucked and slammed Cello-like instrument) the strongest accompaniment I know. "Strongest" in the sense of "supporting the melody" and "maintaining the rhythm". Yet it's so simple (apart from catching it in a style)... ;-)