Yeah, don't do this. Your co-workers will rapidly come to fear you touching their code if you keep rewriting it all the time.

Try and pick up their 'style' if there's a consistent one and code like them. The way they name their variables, etc. If not it'll just take time. The more you touch particular parts of the code base, the more familiar you'll get with it. The more you work with someone else's style, the more you'll be able to parse it.