Is this the way to do it?
1. First do a hard reset pressing *#7370#.
2. Then install OM 3.0 to my phone.
3. And after that uppgrade the phones firmware to v31.0.016?
4. After completed the above mentioned - then I can put back any aplications that I had on the phone prior to resetting?
No it isn't.
Hard reset first in view of UDP = User Data Preservation of your N82
Upgrading firmware to V31.0.016 will revert to not the latest version of Maps v2.0, but should at least then allow clean install of V3.0 Beta.
If you install other applications first you may run out of memory and it won't launch first time around.
Bear in mind that it is also possible to extract Nokia_Maps_3.0_0302_3.1_u.sis if after downloading it using Maps Updater application but before clicking install you search for newly created .sis file on your PC for a normal installation, provided that you delete old map data data in E:/cities and "qf" file first.