Spools of 3dimensional and Prusa seems to be identical. I have upcycled a 3dimensional spool (⌀200x76).
Cut the spool in the middle. To get a constant thickness of the spool, I recommend to use a piece of wood which fits to the inner of the spool to guide the saw blade (see picture).
To spool rest of filament to your new small spool, you could use my suitable spool winder.
The author marked this model as their own original creation.