State law requires that towns assess the value of all properties every five years to see what’s changed, then adjust tax rates accordingly. The last time Stamford did a reval, as they’re called, Cuscuna was among the crowd of angry homeowners that descended on City Hall. The 2012 reval delivered Cuscuna a 25 percent tax hike that heightened the chances she will have to give up the century-old Shippan home where her family has lived for 30 years.