my %hash = ( key => 'value');
  my $k_ref = \$hash{key} ;
  *{'main::val'} = $k_ref ; ## To avoid $$k_ref
  
  print "val: <$val>\n" ;
  print "key: <$hash{key}>\n" ;
  {
    local( $val )= 'test' ;
    print "val: <$val>\n" ;
    print "key: <$hash{key}>\n" ;
  }

##</code><code>##

val: <value>
key: <value>
val: <test>
key: <value>

##</code><code>##

    my $saved= *main::val{SCALAR};
    *main::val= do { my $new; \$new };
    ...
    *main::val= $saved;