well i did it. used a wet saw. cut through the glass like butter. did the long side then two short sides then went to flip the thing over. woops.
ok this is easy. place the tank on a flat surface. rent or borrow a wet saw. cut one long side first. dry the tanks exterior then useing a thin piece of wood, hot glue it to the long side you just cut. then cut the other long side and hot glue a piece of wood to it. cut a short side and do the same with the glue. cut the other short side. carefully remove the the hot glued pieces of wood.
do not do what i did or you will end up with a BROKEN forty gallon breeder. when i flip it, to much stress was placed on the last piece of glass and it broke.