Yes, well, I finally solved it. Thanks everyone for the help! The solution was far from intuitive. It appears first youI join empty, newly created shapefile with the corresponding Excel, and then export the shapefile to enotheranother one, and now youI can edit the values in the atribute table like youI'd expect. As to polygons - it seems they can be created either in the empty shapefile before exporting or after, in the final shapefile already. In my case editing the values had to be done exclusively manually. So I just toggle the edit button in the exported shapefile and I was good to go. Of course I stumbled upon another counterintuitive hassle - although in the new, joined shapefile the names of the fields from Excel appeared correct, after exporting they all got clipped to max 10 characters. I spent a good half an hour just to realize that it's somewhere deep inside the shapefile format, and it actually cannot be solved. So I just left it as is, hopefully my client`ll be able to deal with it.
