moving more than 999 armies

lol i know this sounds crazy, but we had a "cold war" standoff game get up high in the rounds and cards got crazy. Anyway, i don' t know if you know or not, but you cannot move on attack more than 999 armies.
is this by design? and if so, can it be changed? haha
is this by design? and if so, can it be changed? haha