Starting from here:
Just imagine instead of Google drive it is a forum page with a blueprint zip file attached.
IF it is a blueprint.txt and not a zip, you can skip all the stuff about unzipping the downloaded file, and place the downloaded blueprint.txt file directly in a prepared folder you made from SFS.
So if you wanted to download and use a blueprint.txt for a rocket called AnExample, open your SFS, save anything as AnExample, navigate to where the AnExample folder is, delete the existing blueprint.txt inside, and when you download the new blueprint.txt, place it directly in that folder.
A quicksave is 4 files inside one folder, the best idea is to zip up the folder for easy transfer, and make them unzip it after they put it where it should go.