I’ll be flying HKG–ICN on Cathay Pacific, then connecting later that day on Finnair ICN–HEL (separate tickets). I’m Oneworld Emerald, so Cathay allows 2 checked bags, but Finnair only allows 1 bag on my fare.

Cathay is apparently fine with interlining the baggage to AY, but I’m unsure how the allowance would work in practice.

Do I need to pre-purchase an extra bag on Finnair before I check in, or can Cathay handle it at the desk when tagging the bags through to HEL? I suspect they might not be able to collect AY’s baggage fee, but I’m not certain. I'm not sure if I'll even need the second bag, so I was hoping to be able to decide on the day.