1.) Let's say i join a mining group, provide my wallet address, and set the cashout threshold to 1 BTC. My rigs are working, and i reach 1 BTC, and I find that BTC in my wallet. I decide to backup my wallet, so from the computer where the wallet is, i will take a copy of wallet.dat and put it safely on a USB and store it offline.
Now, while my rig is still running, can i update my wallet ID so all new BTCs go to it?
That depends on the mining pool. Generally though, Bitcoin mining pools allow the miner to change their withdrawal addresses at will. If the withdrawal process is scheduled and automated, then just change your listed address before the next scheduled withdrawal.
We can provide you with a more accurate response if you provide us with the name of your mining pool.
2.) If i take a copy of the wallet.dat and store it as explained above, and I run my wallet software again, what happens? does this make my backup obselete?
I would also appreciate if you show me a reference to good topics of backups and advanced backups.
It's a backup. It will contain outdated information as opposed to your current data file, but it will never be obsolete. It will still contain some of your private keys, and it will certainly be useful if it's your latest backup.
As for the topic of advanced backups, all I can say is that a backup is a backup. It's a file. As long as it's a usable (as tested) copy and you have kept it private and secure, then it's a decent backup.
I don't recommend using a backup copy of a Blockchain.info wallet as a cold storage solution though. If you're going to keep a cold storage address in a USB drive, then get one that no other entity has ever had access to.
In all wallet except 1 web wallet(don't know if there is any other), you can generate many addresses.
