1K status with regards to enforcing this rule will mean little to SQ or TG. (I will say though, if you have the highest status level on the partner airline in question you may be able work some magic. I know a Lufthansa Senator who changed their UA MP-issued award ticket for travel on LH, day/date & routing.) The best you can hope for is that you can stand-by on a same day, earlier flight on UA. That is to say, if you had a UA MP-issued award ticket that included travel on UA, you could take an earlier flight on UA the same day, on a space-available basis. I've done this twice.