These are NPL-style flats. They each have 14 words, and each has a base part that refers to one of the 14 senses of the adjective “flat”, as hinted by the title and the flavortext.
Their solutions are as follows:
|Flat def. sense
|Other part of base
|SECOND LETTER CHANGE
|Our hi-pri docs cannot be CLAIR. ’Til CHAIR, we must send mail by air.
|ABHOR, CHORIZO, DENTAL
|Hate open crab? Use sausage anchor. With teeth, grin wide, Not up to rancor.
|Canola is not my suggested choice grease. Instead, extra-virgin GAS ups food’s taste GEESE.
|Keep barn CATSs SCAT on gloves, not sky. In jesses, birds won’t even fly.
|The first two cans’re gloss, but then The pressing TEND: The third one’s TEN!
|REVERSED PALINDROME DELETION
|The drone goes on too long and DIVINE. In END, I execrate its whine.
|Beer, tea, black VIEW all serve to move A singer’s voice to sounding YOU’VE
|I do suggest for older guys To lay EYRES while doc checks your EYES
|SH or the E LED
|I’ve spools and kittens, leather pumps—I think that SOL shoes are for chumps.
|They put up new rugs that are BLAH. That older ones were rough’s LA.
|My horse should have a ROEHRICH? Fair. I’m clumsy on beasts from a CO-HEIR.
|We’re BARE to string it BEAR to shoot, Avoiding your new shoes to boot!
|To PAT down vintners, one just scans For wine ATs detailed in floor plans.
|With negative culture and unchanging voice, I’m BACH and my BATCH dialect’s by choice.
Order by the sense of the adjective “flat” in m-w.com (or the print 11th Collegiate Dictionary) and take the nth word of each flat, where n is the sense of “flat” in each flat. You get:
I open up my leather CHAIR
And move in my new third floor CO-HEIR
The cuewords clue this is a consonantcy. The solution is
PORTMANTEAU. Take the non-“flat” one to get the answer