Interestingly I am in the same boat - I have upcoming work travel to APAC via DL to ICN and KE onwards to my final destination that my company only permits PS. I have GUCs available, so need to force the KE segments in economy into Y/B/M so I can apply the GUC (I have confirmed that for now at least there is KE availability for the GUC in the appropriate fare classes). I basically need DL to re-fare and re-ticket just the KE operated segments to Y/B/M (which I would pay for out of my own pocket). If OP or anyone has been able to successfully do this, would love to hear that data point. To be clear, I can get an entire ticket issued Y/B/M, but the intent is to keep the P/A/G PS class to ICN, and then Y/B/M on KE to/from ICN.The later scenario would allow direct and confirmed upgrade to J using GUC as long as space was available.Thanks.