How do you have your directory and file named for the movie? If you name it with the year in parentheses it should match correctly. In this case, use something like:
Movies/ <--- Library points here, name doesn't matter
Penelope (1966)/ <--- This directory is not mandatory, but it is a good practice to place each movie in its own folder
Penelope (1966).ext
As for locking manually modified metadata, when the lock is orange, the field should be locked (I say should be because if it’s not actually matched it could be removed by a library scan). However, if you get the movie to match correctly, no modifications should be needed.
If it still doesn’t match the correct movie after changing the file/directory names, you may need to perform the Plex Dance:
