Is there a way to restart a chapter with a different end to a previous chapter?

The title is probably confusing, but that's the best way I could think to word it.

My brother beat chapter 3 by killing Tenna, and I spared him; once he realized that I got Tenna in Castle Town, he realized that he also wanted to spare him. He went back and redid the Tenna fight (he hadn't previously saved afterwards) and ACTed this time (he also saved after the fight this time). We deleted his chapter 4 data and restarted with the chapter 3 data in that save slot, but said save was still with a dead Tenna, even though the most recent time he beat the chapter was through sparing.

My question is: is it possible for him to continue his chapter 4 save from the save where he spared Tenna, and if so, how?