Nothing you can really do that isn't obvious.
Best solution is to blank out the original text. Add gen media on upper track, chose color that doesn't stick out too much. Cut it out to hide bad text using mask in event pan/crop, maybe feather the edge.
Add replacment text on track above the gen media.

If it's just one letter that's wrong you might get very lucky and be able to use the above to replace just one letter.

You could also use the above technique to turn your text into a lower third, depending on where in the frame the original text was.

Bob.

IF it helps there are also tools outside of Vegas... I've cut out a section of vid, worked it using the different logo removal plugins for V/Dub for instance, or converted to images and created a P/Shop action to batch process them. Once you have a *clean slate*, overlay the fix & insert back in the video.

To Add to Bobs suggestion

find a frame that has no text ,take a snap of that place that underneath your text layers and do a reverse feathered mask
over the text cutting out the text, correction text on a new layer

If that doesn't work because there's motion try this:

Copy video to upper track. Add enough blur to make the text unreadable then mask out that portion with a feathered edge to hide the original text and add the new text on a track above.

Bob.

just as an aside - whose stuff-up was the mis-spelling?

if yours, you've learnt a lesson the hard way, if someone else's, then i hope you're charging accordingly.

leslie