Finnair takes quite an interesting approach to this. They allow you to use self-service to select alternate flights, but those flight selections are limited to either own flights or certain partners, and the choices change frequently (and may not be in the same class of service if you booked into biz). However, if you contact Finnair agents, they will give the usual partner booking explanation that they can't do anything for you and to contact the ticketing carrier. Having dealt with multiple Finnair partner award schedule changes, the best (and perhaps only) way to move to a different flight is with their online self-service workflow. (According to long-time Finnair agents, in recent years the company has removed the ability of front-line agents to really do anything, and everything gets escalated to a non-customer-facing team at HQ for decision-making.)

I have not seen any other operating carrier allow self-service on partner premium class awards. I have had mixed success contacting either the ticketing or operating carrier, and sometimes one or the other will be able to do something (usually requiring escalation to partner liaisons and then revenue management), but it can get time consuming. When it works, the operating carrier puts you on the flights you want (either by opening their own inventory or using THEIR partners) but does not ticket it, and then sends you back to the ticketing carrier for reticketing. I believe contractually all AS has to do is to offer you a refund, but since award tickets are generally refundable anyway, it isn't too much help. Good luck!