That would make it two different graces, instead of one and the same grace of Baptism.
The grace received through baptism of desire is the same quality as that which is received in absolution. When a person in mortal sin receives absolution, his sins are forgiven, but the temporal punishment for his sin is not. That is, his temporal punishment is not remitted by the grace received through absolution, but it could be remitted if, in addition to absolution, his personal contrition sufficed to remit it.