Results -
Initial condition for $href->{KEY1}={KEY11=>"a",KEY12=>"b"}
$VAR1 = {
          'KEY1' => {
                      'KEY12' => 'b',
                      'KEY11' => 'a'
                    }
        };
Change one key in the hash:${$href->{KEY1}}{KEY11}="c"
$VAR1 = {
          'KEY1' => {
                      'KEY12' => 'b',
                      'KEY11' => 'c'
                    }
        };
Change all keys in the slice:@{$href->{KEY1}}{[qw/KEY11 KEY12/]}=("c" ,"d")?
$VAR1 = {
          'KEY1' => {
                      'KEY12' => 'b',
                      'ARRAY(0x50db350)' => 'c',
                      'KEY11' => 'c'
                    }
        };