Received the correct amount of Bytes as per new rules. Do we have to backup the wallet every time after Black byte distribution as its not registered on the DAG and kept locally?
You don't have to backup anything; however, highly suggested you make backups all the time (specifically after any blackbyte send/receive).
No one ever regretted making too many backups. Most people complain that didn't make a backup when they should have.
My doubt is about how black bytes are tracked and how to get back up and running in case of a hdd crash. Most cases, having the private key of the address is enough if its tracked through DAG / blockchain, but I believe black bytes are transferred P2P with no involvement of DAG / blockchain.