I am pretty certain it is one certificate for each situation (a little bit of extra cash for the government). The form has several tick boxes, but it's only to identify your purpose, so they get it correct on the certificate. If not you could tick every box and use it multiple times.
I have 2 accounts for exactly this reason and as Stuart Cumming stated I also keep about a thousand extra in to ensure it never goes below the immigration threshold.
did I miss that, did he say new passport or re-entering the country? I thought he was talking about changing address, so first report after changing province.
It is really easy to do reports online. I have done all of mine online for the past 2 years, other than one time when I was at the IO, so it was convenient. I have moved provinces twice and had no problems reporting online.
The great thing is you can report online 14 days in advance, if for some reason it was not approved you can go to the IO a couple of weeks later and report. Nothing to lose, so give it a try.