Hi,
i have a light ticket outbound to thailand business class this summer. This includes luggage for 4 people
the return is also light ticket, but premium economy. This flight starts in phuket with Malaysian airlines to KL and than with KLM back to Amsterdam.
here comes my challenge:
- klm phone support can not add luggage to the returnflight, claiming MH is the starting airline
- MH phone support can not add luggage to the returnflight, claiming it is KLM codeshare and they can not modify booking to add luggge.
- logging in with thr PNR on MH site i can see all flight details, but not select seats/ add luggage.

MH says i can buy luggage at the airport, but they can not state a price other than the excess luggage prices (to europe 44 usd per kilo),and with 4 people each having 20kg this would get ridiculous expensive

what would you advise to do?

Tickets involving other airlines as a starting point always cause issues for adding luggage. Typically it's only possible at the airport.

If you're still within 24 hours of purchase, then see if you can still cancel for free.

Next time -when third party airlines are involved in the ticket - be aware that you will probably not be able to add an extra bag until you get to the airport, so instead make sure to buy the type of ticket you actually require (one including luggage in this instance)

Indeed, and elite-perks don't apply either for the MH flight. I avoid these itineraries at all cost even though they're often cheaper than KL/AF-only itineraries.

Unfortunately its more than 24hrs ago. But orginally this flight was booked via jetstar and than SIN-AMS with KLM. With jetstar i was able to login and purchase luggage.
however this week jetstar asia stopped flying, this flight got cancelled. And i was rebooked via MH.
any experience contacting KLM about some flexibility here? This was an involuntary change.

and indeed: never again codeshare flight without luggage.

other question: what would MH charge in this case: everthing under excess prices or would they have a standard bag fee?

KLM would charge you normal advance price for the bags, without the airport surcharge. I am not sure about MH.

For an invol change, you can try to get a better routing.

This changes everything! Like @sehgalanuj said, try to get a better routing, for example with Bangkok Airways. According to KLM website, with Bangkok Airlines the following will apply:
Or if your trip is after November 27, AF will start serving Phuket.

thanks all for replies. I decided to cancel the HKT-KUL leg of the return journey, and only keep KUL-AMS flight. That solves the adding luggage part. Since flight is at 23.55 at night with KLM, i�ll book a morning flight myself from HKT-KUL, to leave 11 hrs of transit time. If all goes allright, we make a short trip to KL center, if not we should have plenty of time to suffer long delays.