How to add a scoreboard to a pre-recorded video file
Have you ever heard the expression: 'Good, fast and cheap. Pick any two.'?  

A good and fast way would be to hire a professional post-production studio capable of layering over the video a scorebdoard graphic, and layering over the graphic a character-generator input. You sit in the chair behind the editor and tell him what scores to input and when. The new edit master would have your scores popping on in sync with the action. This will not be cheap, but you didn't say that you want 'cheap.'

You could also use a programming environment like Flash to layer-on the scoreboard and add sequential cue-points to the video. Then you'd write some code that would insert the proper score at the proper points.

This is, potentially, cheap and good. But you'll need to get some programming skills and that won't be fast.

I think that a better idea would be to realize that good video work, like all good craft, is NOT painless. Just do the work. And, by the way, Adobe After Effects would make this job almost fun.