decimate - remove one in ten (decem)
undecimate - remove one in eleven (undecem)
But that immediately causes the problem that there is now no verb for reversing a decimation. Even worse, a company which announces a decimation, followed shortly by one of an undecimation, is announcing that things are even worse for the their serfs. Whilst El Reg readers are clearly clued up on Latin, the same cannot be said of Sun and Daily Mail readers, or even parliamentarians, so this neologism will serve to have catastrophes praised as U-turns.