I was wondering if this treatment can be used with existing Kevlar ballistic vest panels to extend their usability?

Liquid Body Armor - This liquid body armor is made from magnetorheological fluid, a fluid that remains in a liquid state until the application of a magnetic field. When an electrical pulse is applied, the armor transitions from a soft state to a rigid state in thousandths of a second.

So you need to wire the panels and supply current.
Darn.