What is the musical term for an amended ending where the leading note is flattened and then resolves to the correct leading note? For example, a piece in C Major ends with a Perfect cadence, where the tenor should sing a B natural before the C, but sings a B flat and then a B natural before resolving to the keynote C. Choirs often do this in 16th and 17th century pieces. We did it at school to annoy the music master but he actually liked it!
It's called a 'False Relation'. Nice, isn't it?
We might label it today as a 'Modal Interchange'. Less formally as a 'Blue Note'. Common then, and common now. Maybe not quite so common in the period inbetween.
(PLEASE correct your logo. The bass clef B might require a cautionary natural, but it's no way a sharp!)
(And this is how you put an image in a SE message. Click the indicated button...)
Things were still quite modal in the 16th/17th C, so I'd consider the flat-7 (Bb in C) to be just a normal subtonic in Mixolydian. Even in modal pieces back then one would often use "musica ficta" to raise that leading tone at cadences. Is that the term you have in mind? I'm not sure about going from nat(or flat)-7 --> #(or nat)7 --> tonic, though.