Yes. This is very easy to do. I would advise that this is only good if you have a very simple 'validation'. If your validation has tons of different paths, then it can often be better to go down the assigning variables route.
So... getting to the answer:
On the Screen, each 'field' that you have added needs to have a 'default value' set to the field that is on the Object. That means, you need to have a Record Lookup BEFORE the Screen so that you can pre-populate it with the correct values (unless you're doing all that in your VF Page OR URL).
Now, so we have those fields, they are now populating our lovely Screen! Awesome! (however, this doesn't work as easy with picklists).
Okay, so now when you're on your Record Update, you want to scroll down just a bit further from the variables section, and look for your Screen Input Fields this is where you'll be able to grab the user entered data. IF nothing changed, THEN you'll have the same data as before. IF something did, THEN it'll put that new data in there.