MXO is a scheme and does not dictate wat portfolio one carries.
its for those with degree and above. so you can be be a policy
analyst, corp comms officer, OE officer, etc etc. and all
ministries (other than mindef and moe i think) follows this scheme.
btw, there are also MSOs and CSOs.
as for job rotation, it depends on the scheme u go for too. for
MXOs, u wont be rotated automatically. and even if u get to change
ur job, it wil be within the same ministry unless u go and apply
for another job in another ministry or u ask for secondment.