Changing strings is fine, Dusty, but having them snap is very, very dangerous. I have managed to convince my wife that this is so and she loves me so much that she would rather I bought another dulcimer than risk getting hurt.
This works for me and I am sticking with it.
@jp, I regularly use a .014 on my melody string and almost always tune to d. I've never had a string break on my dulcimer when I was tuning it. But perhaps on longer VSLs .012 or even lighter would work better. I say go for it and see what happens, perhaps putting on some goggles just in case. 
Jeepers, creepers, you gotta protect your peepers!
@nigelbleddfa, it is surely the case that the more you change a string's tuning the more likely the string is to snap, but so what? It's a good idea to change strings every 3-6 months anyway, so I don't see what the big deal is. A string costs a buck. A dulcimer costs a lot more than that. There are better reasons to justify a new dulcimer.
Maybe I'm spoiled. My thoughtful wife 
got me a $100 gift card to Just Strings for my last birthday. I was able to buy several years worth of strings with that.
My first dulcimer was tuned DAD. I told my wife that it was dangerous to keep changing the tuning to DAA and over a period of time strings would snap and replacements would be needed. She accepted this and I bought a second dulcimer which is permanently tuned DAA.
Do you think she will accept the "strings snapping" argument as a good reason for buying a third ? I quite fancy a nice solid walnut one.
ok the good news is yes you can tune it up. it is tight but it is there.... changing strings is not an issue for me ... i wanted to be able to go back and forth DAD and DDD...on the same machine... with out surprises.
thanks to ken for the counsel.....he got closest to a yes or no answer.
I'm with Skip on this one. Strings are inexpensive and easily replaced. Replace the .014 gauge with a .012 gauge.
jp,
You will be increase the tension from ~ 20 lbs [calculated] to ~27 lb according to d'addario string tension chart pdf. Their chart shows the .014 going up to ~38 lbs for an 'f' on a 26 1/4 banjo vsl. You could also replace the A with one of the melody strings or install a new, additional, .012 string.
Maybe it's just me yet I would not try to take a .014 string up to D from an A.
Aye, well, I didn't understand that from your first post, it's true. As Skip says, tune the Middle Drone A string UP to the same d as your melody string(s). A 14 ga string on 26"-27" VSL should be able to tune to d, because you can play that same d on the 10th fret. Then your tuning will be Bagpipe D -- that is Ddd
Tune the 'A' to the same as the melody, dd [middle 'A' to 'd']. You're tuning then will be spelled as Ddd [or Dddd], bass to melody, in MD speak. If you loosen the 'A' to 'D' it will be pretty 'floppy'. The .014 will feel tighter than the 2 melody strings though if those are smaller.
You may be looking at the tuning "backwards". Dulcimer tunings these days are specified from the Bass to the Melody string and we only ever mention the doubled melody string(s) if they are actually tuned differently.
The Bass string is D, your A string is the Middle drone, and the d string(s) are the Melody string(s) an octave higher than the Bass.
On a 26-27" VSL, a 14 ga should be easily tuned to the 5th above the Bass string -- A. Fret the Bass string at the 4th fret, and sound the note -- that's what you tune the Middle Drone string to -- A. Your Melody strings should be a bit lighter gauge -- 12s. Tune them to d an octave above the Bass string D.
BTW -- Bagpipe Tuning is defined as a Bass string tuned D (for example) and all the other strings tuned an octave above -- Ddd for example, not DAd. DAd is the Mixolydian Modal tuning.
