I've always wondered how to make changes in the .pm's that are installed on my machine.

Well, it's possible to patch them directly where they are installed in the @INC paths, but as you've discovered those changes are easily clobbered by a reinstall. So when patching something it's usually better to do so in the distributions before installation. But even in that case there are some chances for conflicts, for example, if you don't change the version number, there is a potential for confusion about whether the patched version is installed or not; and if you simply increment the version number, there is a chance for conflict when the module gets an update by the author. There are several different approaches, listing them all is probably too much, best to cross that bridge if and when you get to it and ask about it then :-) In regards to the question in this thread, note it's about modifying one of the test scripts that don't actually get installed, they only get run before installation to verify that the module was compiled ok on your machine.

Update:

Unable to get Terminal Size. The Win32 GetConsoleScreenBufferInfo call didn't work. The COLUMNS and LINES environment variables didn't work.

See Re: Unable to debug due to terminal problem (read) and Re: Problems starting the debugger