How to modify Citation Style without writing a whole CSL

Hello,

I am helping a friend of mine to setup a template for her Rechtswissenschaften homework.

For that she needs to Cite Laws, Legal Decissions and Law Literature. All the Citations happen as footnotes. For Laws and Legal Decissions this is no problem, as they do not show up in the Bibliography.

For Law Literature this is different. The Citation need to use a shortened Author and a shortened Title.
i.e.: “Bitter, Georg und Röder, Sebastian, Bundesgesetztbuch Allgemeiner Teil” needs to become “Bitter/Röder, BGB AT, ”

After looking at some citation styles I figured, that chicago-shortened-notes gives most of this. Specifically it is a citation style which uses footnotes and uses short-titles.
Yet the Author field is using “und”, the german word for and.

Furthermore in the Bibliography it should say “[Authors], [Title], [Edition], [Year], (zit. Bitter/Röder, BGB AT)” meaning cited shortly as “Bitter/Röder, BGB AT”.

What can I do to make this work without writing a whole custom CSL file. Are there just fields unknown to me that I can use to make this work?