I like this "minced oath" theory.
You had a lot of luck finding it. Finding some colloquial, long forgotten folk saying in a Latin book had little chance to succeed. Sure, now we can see it survived in some forms:
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But without that referrence connecting the dots could be impossible.
It all makes sense to me. There was a medieval tradition of writing some signature or something personal in the last page. See: You are not allowed to view links.
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So all this text would be some magical incantation after writing the book, probably for good luck. Possibly mixing real words and magic words like "hocus pocus" or "abra cadabra".
"Maria" which appears laters makes sense as well. Yes, it is this Maria, mother of Jesus and the scribe is probably asking her for help among others. And he uses crosses to separate parts of the magical formula like it was in tradition.
By the way, I sense something shady about him like others

A pious man would just thank or ask directly God for help in perfect Latin and not talk in some slang used by boors and ruffians. Some forger or charlatan???