No, God still is characterized by perfect justice. One might sin all their life and then enter into a relationship with Him on His grounds, but that doesn't mean one's rewards will be as great as those who remained obedient and bore fruit throughout their lives.
Salvation via unlimited atonement for sin by Christ merely shows that the wrong has been paid for so as to alow a relationship with God. Rewards for eternity are still yet to be addressed until after the Great White Throne Judgement and when the books are opened.
It is not God's justice that is in question, it is the belief that one can really get away with doing wrong and that religion is the trick that does it. The Bible does not teach this, but most versions of Christianity do.
If Bible conversion is correctly understood, it is anything but "free." It cost the incarnate God His life and it costs the convert everything. Anything but total surrender is not regeneration. "Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new. (2Co 5:17)
Most Christians believe salvation is something added on to their lives. Most even talk about, "two natures," the old unsaved nature and the new regenerated nature. If the old nature is not irradicated and replaced with a new nature, it is not conversion, but a superstitious belief in the magic fee ticket to heaven.
One might sin all their life and then enter into a relationship with Him on His grounds, but that doesn't mean one's rewards will be as great as those who remained obedient and bore fruit throughout their lives.
On what grounds does one who, "might sin all their life," receive any, "reward," at all? What are they being rewarded for?
Hank