@nelluk - thanks for the detail, that is
exactly what I needed to know
Before I revisit thinking about your original request, just a suggestion. Steps 6,7,8 could all be done with a single "Add to shelf" click using this plugin. You have the opportunity in the dialog that pops up to:
(a) Specify one or more shelves (in your case the "read" shelf along with your other genre specific shelves)
(b) Edit the rating and date read field
(c) All the above gets pushed up to Goodreads when you click on Add to shelf.
Now if you have setup via the Goodreads Sync Configure plugin dialog the "Add actions" for each of those genre shelves, you could have them assigning the tags value for the relevant genre.
If you do that, there is no need to sync. Ever. Nor is there a need for using the Download shelves as tags option.
Any reason why that wouldn't work for you?