@Rellwood: Are you sending to Amazon (to Kindle's email address?) mobi type "both" (in order to get KF8/azw3 file delivered to your Kindle) or mobi type "old"?
If you're using plain old mobi then you can just use metadata plugboard template which targets format "mobi" and device "email" (instead of the usual "kindle2") to change the title metadata. Then you just send the book using Calibre (Connect/Share > Email to xyz@kindle.com) and plugboards rule will do the title change for you.
No need to "mangle" title metadata for "master copy" file inside Calibre library and revert the changes after sending the book to "cloud".
IIRC Calibre still doesn't do correct job when editing metadata for mobi type "both"( aka "combo" aka "dual mobi") files so you can't use that approach if you're converting to mobi type "both" and sending that...
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