Cool, well done. Sure looks like a vest I had some time ago...

I did the same thing to an old sleeping bag.... I had an 800-fill MHW bag that was warm and light, but I never liked because it was too constricting. Enter a used MHW phantom 45-degree "long" model version I bought for virtually nothing, that WAS large enough in girth, but not nearly as warm. So, with great care I harvested the down from the small bag, put 4 ounces or so (that's a lot of down) into the larger bag, voila, now I had (and still have) a fantastic and very light 25 degree-ish bag. Of course I had to cut slits in a dozen horizontal baffles, but the Tenacious Tape repair to each is bomber. The baffles held the extra down easily w/o being too tight and compressing the down.

2-3 years later, I bought an EE double quilt for my wife and I, but soon discovered that EE is very optimistic on their temp ratings, well, easy to fix, still had plenty of 800-fill down left, and voila, added 4-5 ounces to the EE quilt, now it's toasty warm! What was really nice about the EE quilt is that I only had to make one single slit, and with a 2' piece of 1" PVC pipe and a broom handle for a plunger, I was able to access basically all of the baffles. Same deal, even with the extra down, the baffles were still plenty big.

Dealing with that virtually weightless down is messy though.. always had some cleaning up to do afterwards, and it goes without saying, you really need to do this indoors with zero air flow around.

I used to have a few pics of these down-stuff events, can't find them, alas.