Kitchen light lenses

If it matters, these fit flush with the ceiling and measure something like 21" by 48" (approx; 2 of them)

Yes, you can score and snap them. You can also cut them with any type of saw or router. If you have the type that are molded - and it sounds like you do since you speak of "lenses - score the smooth side.

If what you have are flat plastic lenses like those in 2X4 lay in florescent fixtures seen in offices everywhere, only smaller in size, you can buy 2X4 replacement lenses from one of the home improvement stores and cut them down with a plastic scoring tool like the one I use.

TDD

You may be able to get replacements at an electrical supply company. Another option is a plastics distributor who will cut them to size for you.

Some hardware stores will cut them down for you. Unless they are the grid type, get the acrylic ones. They cost more but the styrene ones are more bittle and turn yellow over time.