Can one switch chazzanim at non-traditional places in the service to accomodate a mourner who came late? For example, Reuven is asked to lead the prayers (say mincha). He says “Ashrei”, “Kaddish” and the quiet Amidah. He looks around to see if sufficient people have finished for him to start the repetition and sees Shimon (who has Yahrzeit that day and came late to prayers) gesticulating that he would like to take over.
For the mitzvah of loving your fellow man as yourself, it seems that Reuven must give way.
Is there any reason why he should not?