jq makes for an elegant plugin (https://github.com/tibbycat/kong-response-transformer-jq) but is there something similar for say sed?
Thinking that a sed response transformer plugin could be created with arrays of strings of sed expressions, but wonder if there is a better alternative?
Maybe we don’t need sed
It seems jq can can do this https://stedolan.github.io/jq/manual/#RegularexpressionsPCRE
First time reading about ./jq , sounds like a neat json utility tool, but I wrote some logic in pure lua awhile back that let me edit json payloads fairly thoroughly to my needs(which i ended up scrapping because it was decided among many that we did not want to lose the gateway being transparent, the moment the gateway performs business logic I think you are treading dangerous water 
). Between your two topics do you have any specific Kong questions yet? To answer your original post no there is no sed like plugin for Kong exactly. They have a basic response transformer plugin which only helps modify a single occurrence value at the root of the json payload.