I have a NAF that’s supposed to be in Bb (A#), but the root is almost a half step sharp. All the other notes are fine. Is there anything I can do to tweak this flute so that the root is in tune? (I can’t send it back to the maker.)
Maybe stick some kind of rush in the bell? The practice need not be limited to pipers; I’ve done it to whistles to flatten sharp bell-notes, and with good success.
Yes, what Nano said. 
As a rush, you can try the old twist-tie trick. Bend at the middle in a sort of “V” shape, and insert into the bell end. If the NAF has “direction holes”, the rush should be above the holes. Experiment with the length of the rush, inserting multiple rushes, etc.
An alternative choke is a ball of blue tack putty inserted into the bore, and flattened against the bore wall to tune the pitch. But putty may be messier in a wood bore if it’s not well oiled.
In either case, you’ll want some sort of length of wire / hook to retrieve the rushes or putty. If your NAF is 2-piece, a cleaning rod or push rod may do the trick.
I would especially recommend smooth-profiled nylon weed-whacker cord: it’s sproingy, robust, you get a lot of it for fairly cheap, and best of all it’s pretty kind to wooden surfaces, so it’s all I use any more. I have one whistle that has a lump of wax in the bell; that works too, and I positioned it at the topside of the bell so as to not impede the outflow of moisture and stuff. I prefer to not go that route, though, as weed-whacker cord is of course cleanly removable.
Yeah, what’s the basic repair kit? Cord, plumber’s tape, blue tack, and Babybel cheese.
You pretty much nailed it. 
I’d add razor blades, fingernail clippers, some kind of bodkin and/or a stout bamboo skewer, a scrubbly-type stick-thing for cleanin’ crap outta the chanter, black cheesewax in addition to the red with toothpicks for application of same, pure beeswax, dental floss for sure, electric switch plate insulation foam, odd bits of cork with no apparent purpose, a stash of hair if you don’t have enough of your own, cyanoacrylate glue, a pencil, needlenose pliers and a small pair of wire cutters just because, and of course the conscientious and civic-minded piper also always keeps a wee board handy for cutting stuff on. Saves the damask.
I’m sure I’ve forgotten something… 
…Oh, yeah: rubber bands.
Yeah, this is fun. I’m going to do a whistle kit thread over yonder.
Oh heck … if we need to fix our personal defects, too, we’re all going to need a much larger kit.
gonna need a van 
Oh, fercryinoutloud. I sport my bald spot with pride and the rest of it is too short to rely on. Hairs are a classic tweak. If your drone guill (reed, if you must ) won’t stay open, one fix is to take a hair and wedge it down between the guill’s body and the tongue. Yes, if there’s a drone plaguing you, you can put hair under the tongue to fix that. Seems a bit allegorical, doesn’t it. Ack. Phfftht.
Besides, with the piper’s box-o-crap, the more esoteric its contents, the more it looks like either you must really know what you’re doing, or you’re basically mad. Either way you’re good to go. A ball of hair? But of course. And if you’re really serious, you’ll have grades of it: human for basic, and cat hair for finer work (both should be long for working ease, so choose your friends and Persians accordingly), maybe whiskers (shed whiskers ONLY, or PETA’ll be on yer @$$ faster’n you can say “cruel and unusual”) for the adjustable fine-to-heavy-duty hair tweaks. Be sure to dust for fleas, please.
It just occurred to me that stuffing some hair into the tenor drone might be a big help in quieting it, too. Brash tenor drones often are a bane to the sensitive piper. See? Gotta think ahead.
horse tail…if all else fails…hang 'em 
I am so not going there. 
NAF out of tune
Aren’t they all?
different scale white man!
I’ve read that the traditional design (or one of them) is equal-sized holes, equally spaced the distance of a thumb-width. So whatever scale that gives you - the now ubiquitous in-tune minor pentatonic being a revival concession. I’ve seen flame wars on NAF boards about hole size vs. hole spacing. Got to fight about something, I guess.
This NAF has plays the natural scale (322222), plus a few accidentals. It’s a little different, but I have been able to noodle out some tunes from my whistle repetoire, such as Suo Gan and The South Wind.
ThortonRose, that exceeds 12 semitones (octave).
Don’t you mean 3:2:2:1:2:2 instead?
(my understanding is that is a type of hexatonic scale of many NAF).
Well, there you go! You’re not out of tune, you’re traditional!
A “standard” modern 5-hole NAF would have a natural scale of 3:2:2:3:2, or in G: G Bb c d f g. The 6-hole NAF allows a scale M6th 3:2:2:2:1:2, or in G: G Bb c d e f g. Basically a gapped Dorian with the 2nd missing.
Tuning a Bell note/Keynote/Fundamental/Root note, is done by changing the bore end hole diameter. If the note is sharp, reduction of the diameter with “Blu-Tack” or other type putty will flatten the note. The reverse is also true. Quena Makers use this technique on short bore Bamboo to lower the Keynote
Tone holes can be tuned in the same manner. If the holes have been undercut, a little application of putty to reduce the diameter will flatten the note. Rolling a piece of fine grain sandpaper into a “cone shape” can be used to sand/increase the undercut to sharpen the note. SMALL INCREMENTS!!!
If you make a mistake, you can correct an oversized hole with clear laquer/nail polish. You can also make a tuning reduction permanent this way too.