I want to know how things like Class::MethodMaker and similer things work. Class::MethodMaker creates the subs at compile time. Is it possible to add subs during run time?

Yes, it is possible to do this at runtime. Basically you need to access the symbol table, which can be done like so (altering your code somewhat).

sub add_method {
    my $class = shift;
    my $name = shift;
    my $code = shift;
    no strict 'refs'; # because you should have strict on
    *{$class . '::' . $name} = $code;
}
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Then you can do the following:

# you must call this as a method, and pass it a CODE ref
blort->add_method('foo', sub { print 'bar' });

# now you can do this ...
blort::foo();
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Of course there are a number CPAN modules you could use to do this; Sub::Install, Sub::Installer, Class::Accessor, etc.