Here is something you can try if nothing else has worked:
- go to /var/lib/dpkg/
- take a backup copy of the ststus file: cp status status.BAK
- edit that file: vi status
- search for a line beginning with "Package: mp-harmattan" (I think in your case will be mp-harmattan-232-pr)
- six lines below there is one like: "Version: 40.2012.21-3.232.05.2"
- edit that line so that version is e.g. 41.2012.21-3.232.05.2
- save file and exit from editor
- check for package upgrades again

What should happen is that now the upgrade system believes your device version is 41.something, and what is available is 40.something, a lower number so there is no upgrade for you.
And it should make the green notification disappear.
Should be there any further official upgrade it will very likely have a version number bigger than 41 so you won't lose any real notification. Just in case...

I briefly tested with my device, by bringing first the 'faked' level down, checking upgrades, which has shown the 40.something available on Nokia servers.
Then I raised again the level to the original and rechecked for available upgrades and the notification has disappeared.

It would be also a good idea before you do that to double-check why you get that notification.
Just run "apt-get policy mp-harmattan-232-pr" and compare Installed: and Candidate: fields.