I think that's presumptive. Like one has God in a box in his pocket. God has to forgive him no matter what he does, thinks or believes, no matter if he repents for it or not.
You have a very odd concept of grace.
If you accept Jesus Christ as your Savior, your sin debt has been paid. It cannot be paid any other way. So yes, my sins are forgiven.
But, that does not mean there are not consequences on this earth and in my eternal life if I do not choose to follow Christ after my conversion.
If I kill someone, then I will be held accountable. It does not mean I will not enter heaven if I truly accepted salvation, it just means the rewards there will not be what they can be. And it means I will lose out on the blessings this life will bring me and those around me.
So yes, I should repent for the sins that I commit after salvation. But those sins will not separate me from the love of God or negate His promise of eternal salvation.