Did the plan of salvation change after Christ died?

Did the plan of salvation really change after Christ died? I mean Christ forgave sins when he was alive. The usual proof text one receives is that it is to show that Christ had power to forgive sins while he was on earth. I agree. But does that preclude Christ from forgiving sins the way he used to in the flesh. Before he was born, he was in the Spirit, and people in the O.T were saved by grace through faith (Acts 4:12). So after he was resurrected and went to heaven, why cant he forgive sins as he used to in the O.T. times.
In the O.T. God gave the Israelites laws to obey. But in the N.T - which is supposed to be far better than the O.T. - one has to comb through the entire N.T. to find out the plan of salvation as well as rules of worship. I find this very silly.
And on top of this in 1 Jn 3:23 it says the only commandments we received are to 'belive in Christ' and 'to love one another'. And this was written after the supposed plan of salvation was revealed to the apostles at pentecost. No command of baptism or rules of worship. The only acceptable worship is 'worshiping in truth and in Spirit'
Also read 1Jn 5:1,5,13. Jn 3:36 is very similar to 1Jn 3:13. Both were written by the same author. Seems to me the 'plan of salvation' mentioned in the Matthew,Mark,Luke and John is the same after the the pentecost.
The biblical plan of salvation is - 'believe in the Lord Jesus Christ and you shall be saved'. Note here that to 'believe in someone' is to trust someone completely. It is different from 'believe someone'. For example when someone tells you that the earth is round you believe him. But would you trust him with your soul? Hopefully not? Unless it is Christ.
Luke 24:47 (NASB - 'eis' = for)is this what Peter means in Acts 2:38? I think so. Isnt it odd that Christ before he left the earth would give a plan of salvation that would be different from the one the apostles received at pentecost. Didnt he know it would change? or did he forget? or was the plan always the same?