I'm currently booked on an award ticket FCO-HEL-LAX with a 1 hour layover. I now would like to fly out of BLQ the day prior, but the LAX flight does not operate that day, so I would need to do an overnight in HEL, which I'm willing to do. But is this a legal change to an award ticket or is it now viewed as a stopover that would require separate payments for each segment?

Current booking:
Day 1 FCO-HEL-LAX

Desired booking:
Day -1 BLQ-HEL (HEL-LAX does not operate on this day), connecting to
Day 1 HEL-LAX

Note that on Day 1 there is a normal connection available BLQ-HEL-LAX, if that makes a difference, but I think for most airlines what matters is the connections available on your desired departure date.