Some Jews are upset that Mormons are posthumously baptizing Holocaust victims.
If it makes someone of any faith feel better to baptize me posthumously, or really perform whatever ceremony suits your religious beliefs regarding me in an effort to make sure I’m going to heaven, please feel free to go ahead. It won’t change my eternal destination one iota. Nor do I really think that any posthumous baptism would “change my identity”-my life is the way I live it, and sprinkling water on me after I die won’t change that.
Such posthumous baptism may, however, give the baptizers some measure of peace (however false I believe that peace to be), and if it makes them feel better, they should go ahead. No downside to me.
Of course, I also think that after I die, science should take all my organs, cut me up, and generally use my body to the maximum benefit of the living, so perhaps I am an outlier on this issue.