Before I give my advice I will give you a background story to my knowledge in this subject...I am a certified welder, I used to own a custom car and motorcycle shop building wild lowrider trucks and motorcycles two of those lowrider trucks have been on the cover of DUB magazine. I have welded aluminum, steel, stainless, I have also welded automotive frames so that they could be strong enough to take the abuse of hydraulics and the fun that goes with that sort of setup.

Now on to my answer.....The weld was obviously done by a professional if they do chassis welding on automobiles, not to mention that they have to be certified welders to be doing that sort of work, so that would lead me to believe that the weld was done correctly. It is perfectly safe to file it down to match the contour of the surrounding metal.