Not sure this is helpful, but you can put the playhead over your existing recording and "split" the recording, then do a compute lipsync from the last bit.
After that, I *think* you can delete the second section and grab the right edge of the first audio and stretch it back out again. Splitting does not actually split the audio track, and trimming does not trim the audio. The take in the timeline points to the audio file with a start offset and length (I think!). So you can do tricks like split the take (creates two takes pointing to different parts of the same audio track) then just stretch out one of them to get back the full original take!