If the file names are of the same length, you can just walk over them character by character and keep only those that are different.

#!/usr/bin/perl
use warnings;
use strict;

my @files = qw(
            hhk_1sss-(hello).txt
            hhk_2abc-(hello).txt
            hhk_3xyz-(hello).txt
            );
my @short = @files;

my $pos = 0;
my $file = shift @short;
while ($pos < length $file and '.' ne substr $file, $pos, 1) {
    my $char = substr $file, $pos, 1;
    if (@short == grep $char eq substr($_, $pos, 1), @short) {
        substr $_, $pos, 1, q() for $file, @short;
    } else {
        $pos++;
    }
}
unshift @short, $file;

while (@files) {
    my $old = shift @files;
    my $new = shift @short;
    print "rename $old $new\n";
}
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