That guide I posted also has an offline downgrade/upgrade section. I think from where you are you can just do steps 1-3 and 10-12 on that (making sure to use the right systemmenuv###.wad for your region.
If you really just want that one IOS you should be able to just install that one provided you find the right one that you need. Just don't try to uninstall stuff if it didn't do what you need it to do. Only reinstall over IOS's, don't delete and try to install again.
Also as I said in the last post if you're afraid of bricking, look into bootmii, read up on it, install it to boot2 if you can.