For the last FRWSTAR tickets I've got the option to book with every carrier involved into the PNR.
However, it clearly makes a difference with whom to book because LH has been granted some exceptions from IATA rules. The most helpful relates to changing the first segment of that PNR which is possible on LH issued tix. It saved me tons of money once when my feeder flight to ICN on a seperate PNR caused a serious delay.