Even though there is no compensation under EC 261/2004, the passenger options remain. OP may take a refund, a rebooking around the time of the original flight, or at a lter date. All at OP's option. SK might honor a request to rebook on another carrier, but there is no requirement that it do so.
Before doing anything with SK, why not price the *A alternative. If it is cheaper, then cancel the SK ticket and purchase the new ticket and save.
The worst that can happen if you ask is that the answer is no and you then have a decision to make as to whether you take the refund or pay out the difference.