Overriding pre-defined GraphQLSchema resolvers (Apollo)

Question

I'm setting up a GraphQL wrapper for an existing REST API. The tool I've decided on lets you easily define the way in which all calls to the REST API will be made and generates resolvers for each endpoint.

I would like to be able to override certain queries or mutations with custom logic and I have a hunch it's easily possible with some graphql-tool, but I just haven't landed on it yet.

Below is the main code setting up the server, followed by the fetching client used to query the REST API, followed by the way in which I would like to be able to extend certain endpoints.

// The main server setup thus far

import express from "express";
import cors from "cors";
import { createServer } from "http";

import { callBackend } from "./connections";

import { createSchema } from "swagger-to-graphql";
import { ApolloServer } from "apollo-server-express";
import { generateTypes } from "./utils";
import { parse, printSchema } from "graphql";

const port = process.env.PORT || 4000;

(async () => {
  const app = express();
  const server = createServer(app);

  app.use(cors({ origin: "*", credentials: true }));

  const schema = await createSchema({
    swaggerSchema: "URL_POINTING_TO_SWAGGER_DEFINITION",
    callBackend,
  });

  await generateTypes(parse(printSchema(schema)));

  server.listen(port, () => {
    console.log("Server has launched..");
  });

  const apollo = new ApolloServer({
    introspection: true,
    debug: true,
    tracing: true,
    context: ({ req, res }) => ({ req, res }),
    schema,
  });

  apollo.applyMiddleware({ app, cors: { origin: "*", credentials: false } });
})();

_________________________________________

// The callBackend function being imported in the previous code.

export async function callBackend({
  context,
  requestOptions,
}: CallBackendArguments<Request>) {
  return axios({
    method: requestOptions.method,
    url: `URL${requestOptions.path}`,
    headers: requestOptions.headers,
    params: requestOptions.query,
    data: requestOptions.body,
  });
}

_________________________________________

// The way in which I would like to be able to override certain calls being generated by the
// swagger tools createSchema function. These ideally just get passed into ApolloServer's args as 
// { resolvers: [CustomerResolvers, ...etc] }

export const CustomerResolvers = {
  Query: {
    get_customers(...args) {
     // some additional logic
    },
  },
};