How can I renew an expired domain name though it is in a redemption period in godaddy.com?

If you do a "WHOIS" and the status says it's on redemption period, only the last registered name holder can "redeem" it with the last sponsoring registrar (Go Daddy based on what you stated). Even if you "pretend" to represent the registrant, Go Daddy will still redeem and put it on its last registration account and not in another.

Next best thing is to make a reservation with various backorder companies like Snapnames, Pool, and Enom Club Drop. They have the best batting averages for .com.