Go to Tools>Folder Options in Windows Explorer.
Click the File Types tab.
Under the extensions column, look for PL.
Click the "Delete" button.
Then press the "New" button.
Enter "PL" in the "File extension:" box, then click OK.
Once it appears in the list, click "Advanced", then click "New..."
For action, type "&Open".
For "Application used to perform action:", input the path to your Perl Interpreter, then %1, along with any parameters if necessary.
Example: C:\Perl\bin\perl.exe %1
Then click OK.
"Open" will appear in the list. Now click the "Set Default" button.
If the button is disabled, just click "OK".
Click "Close" again when you are done.

This fully repairs the icon of the file type itself.