Practical way to hack an installed module. "Practical" not good.
Copies a module from your installed module path so you can hack it. It handle a hierarchy of modules under the top module. Or so it says, a quick look at the code tells me it doesn't and the test are not there to check that case.
Environment variables suck, doesn't matter how smart you think it's going to be to use one.
it's cool to discover that Perl allows "my" a bit everywhere but is:
@inc_filenames ? my $inc_filename = shift @inc_filenames : croak ".."
really better than:
my $inc_filename = @inc_filenames ? $inc_filenames : croak "..."
my $inc_filename = $inc_filenames or croak "..." ;
In any case, and not because of this module, this is going to be a real nightmare when people forget to deliver their hacked modules.