Is there a way to clear the previously analyzed text from a clip? So you can start over from scratch.
The speech analysis metadata is written to the clip's XMP ("Extensible Metadata Platform"), which can be written either to a sidecar file or embedded in the video clip, depending on the type of clip. I'm not aware of any way within Premiere Pro to clear the speech analysis text.
If you're dealing with XMP sidecars and--you're comfortable editing an XML file--then you could try making a copy of the sidecar, changing the extension from "xmp" to "xml," manually deleting this content, saving, and changing the extension back to xmp.
But if by "start over from scratch" you mean that you want to have PPRO re-analyze the speech, then it's not necessary to clear the existing speech metadata. If you run speech analysis again, the new results should simply overwrite the earlier results.
I'll try out the XMP idea when I have more time.
I was re-analyzing, but it didn't appear to be replacing the text correctly.
I'll reply when I have a chance to try both options more deliberately.