Technically no.
However you can apply for excuse from your OC for the period of time you going overseas with the reason. Write in to your unit. Case by case basis, OC will exercise their discretion to approve or reject.
Cause if have mob and activated, and you are overseas without official excuse from your OC, you may get charge. And we cant really use the reason of "i plan way ahead for this overseas trip", cause mob manning alert is disseminated to us 6 months prior.
Hope this info helps