Okhttp newBuilder per request

Trying to implement okhttp the correct way. I understand the OkHttpClient must be shared (Singleton), however I am not clearly understanding .newBuilder();

Sample Code:

// Instantiated once
private static OkHttpClient client = new OkHttpClient.Builder()
        .readTimeout(readTime, TimeUnit.MILLISECONDS)
        .connectionPool(new ConnectionPool(200, connectTimeout, TimeUnit.MILLISECONDS));
        .build(); 

public static String makeRestCall(String url, String data, Interceptor customInterceptor) {
    // Questions on the line below
    OkHttpClient newClient = client.newBuilder()
        .addInterceptor(customInterceptor)
        .build();

    ....
    try (Response response = newClient.newCall(httpRequest).execute()) {
            final ResponseBody body = response.body();
            return body.string();
    }
    return "NO_DATA";
}
 

I have a few questions around .newBuilder()

1. When we add a new interceptor to newClient, does the original client also get updated by reference?

2. Classes calling makeRestCall decide on what customInteceptor they need. Is it ok to call .newBuilder() for every request?

I have been searching the documentation and playing with the implementation but haven't had clarity on the above.

Any assistance/pointers are appreciated.