package My::HTTPRequest ;
use base qw/HTTP::Request/ ;

sub new{
   my ($class) = shift ;
   my $self = $class->SUPER::new(@_) ;
   $self->{'myA'} = undef ;
   return bless $self, $class ;
}

sub myM{
  my ($self) = @_ ;
  ...
}

...

1;

##</code><code>##


my $httpr = AnotherModule::f() ;
# $httpr is a plain HTTP::Request object

my $ownHttpr = transform($httpr) ;
# $ownHttpr should be an instance of My::HTTPRequest with all the properties of $httpr .