Any examples of what that might look like?

Basically I just googled how to append to an exiting array. https://stackoverflow.com/questions/29319801/how-to-append-a-new-item-into-the-array-type-column-in-postgresql is one hit. Then you put that in a function with an input parameter of the type you want, use SQL language for the function, and one of those statements with the input parameter as the value. Then call that with rpc call.