lib.pm isn't very large or complicated - how about making a copy with a new name (lib::append, maybe?) and replacing the unshift(@INC,...)s with pushes? And perhaps add a couple of reverses if you want duplicate-removal to leave the last instance of a directory instead of the first:

    # remove trailing duplicates
    ## @INC = grep { ++$names{$_} == 1 } @INC;
    # remove leading duplicates
    @INC = reverse grep { ++$names{$_} == 1 } reverse @INC;
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