Here’s an article about writing freeform LARPs:
freeforms.org.uk/article-fre … ocess.html
“Freeform” is a name used in the UK to refer to LARPs like the Chicago 1930s game that ran a little while ago in Auckland. They’re games where all the characters are written by the organisers and tie into each other, and where typically all the important interaction is between player characters.
In the USA the term “theatre-style” refers to something similar.
I’ve run a couple of games like this, and the advice in the article seems pretty reasonable as an overall structure for going about it, although it doesn’t give much advice about the actual writing.