How do I add more than ~30 signatures to Apple Mail?

I have a lot of signatures, since I like to include witty or insightful quotes at the end of my emails. I was adding them to Apple Mail today and once I get to about 30 or so the list of signatures starts to disappear, like so: I tried to work around this by looking for the plist to edit them, but Apple seems to have closed off ~/Library/Mail, even to the superuser. I know I can delete signature using the - button, and I can still add them using the + button, but I can't edit their names. How might I add more signatures & edit their names?