I'll explain a method to convert default large cube bricks (shown in the image below) to modter bricks of the same size.
Open the .bls save file in Notepadd++ and type "ctrl+f". Go to the "Replace" tab.
At the bottom of this page, set "Search Mode" to "Regular expression."
Find what:
^(8x cube)("\s-?[0-9]\d*(\.\d+)?\s-?[0-9]\d*(\.\d+)?\s-?[0-9]\d*(\.\d+)?\s-?[0-9]\d*(\.\d+)?\s-?[0-9]\d*(\.\d+)?\s-?[0-9]\d*(\.\d+)?\s)(\s)
Replace with:
\1\ \2\ModTer/brickRAMP
****NOTE**** YOU MUST HAVE 1 SPACE AT THE END OF THE ABOVE LINE
Select "Replace All"
Repeat for 16x, 32x, and 64x at the start of 'Find what:' instead of 8x