It's ugly, not golfy, and not fast, but that's the best I could come up with:

my $number="8i8jkwdz4fks4d1z";
chg(1);
sub chg{(substr($number,-1*$_[0],1)=dig(substr($number,-1*$_[0],1))) e
+q '0' and chg($_[0]+1)}
sub dig{my $d=shift; if($d==9){return 'a'}elsif($d=~/\d/){return $d+1}
+elsif(lc($d) eq 'z'){return 0}else{return chr(ord($d)+1)}}
print $number;
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