Greetings,
When I do voiceovers I occasionally make errors that my editor catches. When I go back to re-record, the edited portions of my work are painfully obvious. Is there a tool in audacity that helps with this?
What’s obvious about it? Is there a click or glitch where you cut/splice? Are the levels different? Is the sound character somehow different?
It’s the sound level, my edits always sound louder or softer.
If the retake is too loud or too soft, drag-select the retake and Effect > Amplify. Just hitting OK on Amplify makes the selection as loud as it can be. See http://manual.audacityteam.org/o/man/amplify.html .
If a plosive is in the selection that looks like a spike you may not be able to amplify very far. It would be better to re-record that if you can.
If you are not already doing so, make a defined setup to record from. Same mic at the same height in the same environment. Same pop filter. Mark a spot on the floor where you always stand.
Gale
I agree with Gale, that it’s best if you can kep a consistant setup and learn to make a consistant performance. In the old days of analog tape, we would watch the meters and get the levels right before hitting “Record”. (We also tried to avoid editing as much a possible, since it was done with a razor blade and splicing tape! 
)
Do you use headphones? It might be helpful if listen to the old/previous recording in your headset first so you can compare to what you are currently hearing and try to match the current “live” sound in your headphones. (It’s best/easiest if your hardware allows direct zero-latency monitoring, rather than monitoring through the computer.)
Audacity’s Envelope Tool should be helpful too for manual adjustments after editing. You can try a FREE program called [u]The Levelator[/u] to automatically even everything out. But usually nothing is as good as the human ear, so manual adjustment may be best, or maybe adjust everything manually and then run it through the Levelator.