Yes and no. While DIY Splashbacks only sell toughened glass splashbacks (along with many other splashback materials), once they have been toughened they cannot be cut.
Glass is toughened by superheating it to over 400C in a furnace/toughening plant, this is also why they are so heat resistant. After they are superheated the glass is then rapidly cooled and the end result is glass that is incedibly hard to break (believe us, we throw our rejects into skips and very rarely manage to break them). What actually happens during the toughening process is the outer surfaces are compressed but the inner structure of the glass is put into tension- if you can imagine lots of little molecules all pushing against the surface of the glass providing strength to the outer "shield". This "shield" with all that force behind it is what is pushing against the surface of toughened glass when it is struck.
What happens then when you breach this shield by cutting it? All the little molecules held back by the "shield" are then released causing the glass to crumble. It does though crumble into very small little cubes rather than shards and injuries are incredibly rare- this is why it is used in car windscreens, bus stops and is also known as toughened safety glass!
A photo of broken toughened glass
What happens if my splashback is a little too wide or a little too high, what can I do?
If you have incorrectly ordered and you find your splashback is a little too wide the simple solution if possible is to reomve your kitchen cabinet end panels, fit the glass and refit the end panels. The chances are you will need to trim a little from the back of them so you may need a kitchen fitter to do this for you but we supply and fit many jobs where we deliberately do this as it's a neater finish.
If your splashback is a little too high it depends how much is it off by. You can usually unscrew the bottom teo screws inside your cooker hood (near the bottom) and budge it up a little for small measurements in a matter of minutes. For larger meaurements the extractor may need to come down completely and be rehung a little higher. Again though, we would recommend you use a kitchen fitter to carry out this relatively simple job.