From what I could see from the procedure at the polling booth in the Ngatangiia electorate, rigging the vote would be next to impossible
For one thing there was a police officer at the front entrance to ensure the security of the process.
Intending voters had to report at the front desk located on the verandah (a police officer was stationed there), where we gave our name to be checked against the roll.
There was quite a queue of people and there were several electoral officers manning the front desk.
When our names were confirmed on the roll, we were given a slip of paper with what I presume was our Voter ID number.
Next, we proceeded to a second desk with several other electoral officers who were positioned at the very entrance to the hall.
At the second desk, we handed over the slip of paper and our names were called out loud as they were rechecked on their copy of the roll.
On the left side of the entrance, scrutineers were seated at a separate desk.
After the reconfirmation of our names, we were allowed to proceed to the screened counter set well away from anyone right in the middle of the hall.
We were given instructions to fill in our ballot papers, then to fold them and place them in the ballot box.
Once we had fulfilled our civic duty we left the premises to go about our day.
After having to run the gauntlet under the intense watch of a police officer, several electoral officers and scrutineers, does anyone seriously suggest that it is possible to rig the ballot and cast a vote three times?
The other scenario of voting while not registered is possible, but subject to special conditions.
Funnily enough, there was a lady in the queue just before me whose name could not be found on the main roll.
When asked whether she had registered on the roll, she couldn't remember. They asked other questions, but as I was more concerned about my vote than keeping tabs on others at the polling booth, I don't know what happened in her particular case.
However, in Australia, the electoral office recognises the possibility of a clerical error in the registration process.
Therefore, if you state that you are enrolled and can't understand why you are not on the roll, they do allow you to cast your vote (as a special vote) subject to a later search by the electoral office as to whether or not you are really registered,
It is found that you are not registered, the vote is discounted as null and void for the ballot.
In the Cook Islands context, it is probably the same situation.
After all, you certainly cannot cast a vote after the polling day, under any circumstances whatsoever.