Sash replacement kit question

Hi all, I am currently treating a lot of rot and termite damage outside of the dining room of my house. I have removed the top and side brick mold from 5 windows, plus quite a bit of Masonite hardboard siding. The windows are being held in on the outside by 1/4 - 5/16 strips of wood that came with the old windows. I have ordered replacement sash kits while I'm at it, since these windows have leaked air tremendously since I bought the house 6 years ago. The house is 12 years old. I don't want to install them from the inside, because we spent the last several months caulking and painting the interior of the den/dining room with burgandy walls and white trim to perfection. I refuse to mess that up. My question is, is there any reason that I can't install these sash kits from the outside? Anything I need to be aware of? The old windows and the sash kits are MW windows. I called MW and the only guy who they say can answer my questions never called me back.
Thanks, Stuart

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