Example evalscript where the output is multiplied by 1000.

eval_multi.js

//VERSION=3
function setup() {
  return {
    input: ["B02"],
    output: { bands: 1, sampleType: "UINT16" }
  };
}

const f = 10000;

function evaluatePixel(sample) {
  return [f * sample.B02];
}