import { Prefab } from 'att-string-transcoder';
// ...
const commandResult = await botClient.send('...');
const saveString = commandResult.data.ResultString;
const prefab = Prefab.fromSaveString(saveString);
prefab.setOnFire();
const newSaveString = prefab.toSaveString();
await botClient.send(`spawn string-raw ${newSaveString}`);