I would say yes, if you are experienced in sewing. But if it were me, I would order some 1.1 oz. sylpoly from ripstopbytheroll and make a copy of the annex and put a zipper in it. And the stove jack if I wanted.
Then the integrity of the original annex remains. And you now have options. I had a paratarp with annex and used it for awhile with stove. I then stopped using the stove since I was hunting archery. Then the annex stayed home after it seemed like it was not necessary unless weather might be a problem.
Just my two cents.
My biggest issue with the Velcro on the Kifaru annex was that it required 2 hands to get it closed. Also I never trusted the way the grommet on the annex was supposed go over the trekking pole tip and nest into the Hypalonon the SuperTarp. Seemed like I was always one big wind gust away from a hole in my ST. Lastly I didn’t like running a stove in an ST as it was just too cramped and figured it was just a matter of time before I burned a hole something.
I went a different route and had BPWD put together a custom annex without a door or stove jack. It simply uses a SR buckle on the left and right sides of the bottom making it quick and easy to get in and out. I had him use a loop of grosgrain webbing at the peak that slides over my trekking pole tip and locks into the Hypalon pocket on the SuperTarp much more securely. Not having a door and eliminating the stove jack saved a couple of ounces too. I won't miss the stove jack for my uses and if I want to run a stove I will take my SO Cimarron or Kifaru 8 man.
Looks great. I have a couple questions if you dont mind. How are the sides of the annex attached to the ST? What is the distance between the front and back poles, length wise?
I tried a floorless shelter in the Mountain Smith LT and I had to stay on one side or the other of the poles. Seems to keep sliding out the bottom, side of the tarp after a while.