var %x += 10 (var %x = %x + 10)
var %x -= 10 (var %x = %x - 10)
var %x *= 10 (var %x = %x * 10)
var %x /= 10 (var %x = %x / 10)
var %x ^= 10 (var %x = %x ^ 10)

These would preferably also work if you don't use the /var command.