Yes, it is possible! Toughened glass is produced by heating the glass in a furnace at stable temperature between 620 to 650 degrees Celsius, then rapidly cooling it.
Tempered and heat strengthened glass are both similarly produced. The difference can be found in the cooling process even though both products are force cooled to create center tension and surface or edge compression. With tempered glass the cooling process is accelerated, creating higher surface and edge compression. Surface compression of at least 10 000 PSI and a required edge compression of at least 9 700 PSI. This makes tempered glass between 4 and 5 times stronger than untreated glass.
The value in this is increased safety.
The down side of this process is the fact that the glass needs to be cut to required size before going into the furnace. Once cooled the higher surface and edge compression will not allow the glass to be easily cut without shattering. But all is not lost! Through a process called annealing the glass can again be cut. The basic concept is to reheat the glass to around 500 degrees Celsius and allowing it to cool slowly. This will reverse the toughening process making it possible to re-cut the glass. After cutting, the glass once again needs to go through the toughening process.
*The process described in this article is a highly specialised process and very few companies offer this service. But it can be done!