I'm trying to understand the Base 58 WIF number. While messing around with importing on blockchain I noticed that if you change the last five (or so) digits, it doesn't appear to affect which address is imported - i.e. i get the "This address is already present in the wallet" note. Does anyone have any insight they could share about this?
The last 4 bytes of the WIF format is a checksum. The details can be seen here: https://en.bitcoin.it/wiki/Wallet_import_format
That's approximately 5 characters of Base58 that are essentially redundant. This is so that errors in the WIF encoded private key can be detected easily. I believe some wallets will simply ignore the checksum if it's not correct.