I learned that the one who does Tshuva from love - not only are his sins forgiven, but they are transformed into merits This concept I am trying to understand more clearly. Are the sins themselves turned into merits? or are they consdered merits only because they are inextricably linked to the later Tshuva and are in large measure the motive force propelling him towards Hashem? For instance, let’s say a Jew murdered another Jew, G-d forbid, and because of his remorse he does tremendous Tshuva out of love for Hashem. Without the jarring experience of committing the murder, the Jew would never have done Tshuva. So that event now has a positive aspect to it. But do we say that the murder itself is turned into a merit ie. Do we say "He did a meritorious act by murdering another Jew?"
It is clear to me that a sin can't be called a merit. In your case for instance, murder is bad, even if succeeded by a great Tshuva. It is in the heavenly count; the sins, not only they don't count as sins, they are counted as merits, the explanation can very much be like you explained. Rav Yakov Moshe Charlap in his book Ori VeYishi follows the same concept.