Is it possible to alter a number of cell border thicknesses in one go?

I have a large spreadsheet of sheets containing cells with borders that produce a building map. After making them I have decided to use a thicker line for the external walls. Is there anyway of altering, say, with a macro, the thickness of all the walls in one sheet to another thickness?
I could do them one at a time but there are now so many it would take days of work.
zone2.ods (12.2 KB)
the file just holds a set of borders, I would like some way of converting the left box into a box with the same thickness as the right box. Easy to do here but I have a large number of sheets with much more complicated boxes than here. Is it possible to do with, say, a macro?

Are tose building maps regular rectangles, squares? Or they are some special shapes?