I have seen this used with other words besides "large" and "small". What other words can be used? Can this structure be used more generally with other adjectives?
"Writ" as a verb is an archaic form of "written", the past tense and past participle of "write".
Hence it will take any adverb that applies to writing.
"Writ quickly", "writ slowly", "writ convincingly", "writ badly", etc.
However, I don't recommend using it, except for the idiom "writ large".
I believe that "writ small" and "writ large" can be restated (with some adjustment of the word order) as "a small version of" and "a large version of", respectively.
I don't think this construction can generally be used with other adjectives, though. For one thing, since "writ" is a variation of "written", you could only use adjectives that might also apply to manner in which one writes something. For example, "a mammoth is an elephant writ hairy" wouldn't make much sense. Even if the adjective could apply apply to penmanship, it sounds wrong. For example, "a Granny Smith is a Red Delicious writ green" sounds ridiculous, even though you could theoretically write using green ink rather than red.