When this type of question comes up, I find I'm rather quick to "use the source".

sub Load
{
    my $this= shift(@_);
    my $tied=  ref($this)  &&  tied(%$this);
    $this= tied(%$this)   if  $tied;
    my( $file, $subKey, $opts )= @_;
    if(  2 == @_  &&  "HASH" eq ref($subKey)  ) {
        $opts= $subKey;
        undef $subKey;
    }
    @_ < 1  ||  3 < @_  ||  defined($opts) && "HASH" ne ref($opts)
      and  croak "Usage:  \$key= ",
             "${PACK}->Load( \$fileName, [\$newSubKey,] {OPT=>VAL...} 
+);\n",
             "  options: @Load_Opts @new_Opts\nCalled";
    if(  defined($opts)  &&  exists($opts->{NewSubKey})  ) {
        $subKey= delete $opts->{NewSubKey};
    }
    if(  ! defined( $subKey )  ) {
        if(  "" ne $this->Machine  ) {
            ( $this )= $this->_connect( [$this->Machine,"LMachine"] );
        } else {
            ( $this )= $this->_rootKey( "LMachine" );    # Could also 
+be "Users"
        }
        $subKey= "PerlTie:$$." . ++$Load_Cnt;
    }
    $this->RegLoadKey( $subKey, $file )
      or  return ();
    my $self= $this->new( $subKey, defined($opts) ? $opts : () );
    if(  ! defined( $self )  ) {
        { my $err= Win32::GetLastError();
        #{ local( $^E ); #}
            $this->RegUnLoadKey( $subKey )  or  carp
              "Can't unload $subKey from ", $this->Path, ": ", _ErrMsg
+, "\n";
            Win32::SetLastError($err);
        }
        return ();
    }
    $self->{UNLOADME}= [ $this, $subKey, $file ];
    $self= $self->TiedRef   if  $tied;
    return $self;
}
[download]

Which boils down to a whole lot of error checking and DWIM and other nonsense and

$this->RegLoadKey( $subKey, $file )
[download]

so just do that. See Win32API::Registry for more on this method (note that you can use nearly any Win32API::Registry method directly on a Win32::TieRegistry object, as documented).