How do I import a title screen?
That's easy! Importing a title screen is the same thing as importing a backdrop. First ensure that your title screen is saved as a 320x200 24-bit bitmap (BMP) file. (8-bit also works)
Then, launch custom.exe. Go to Edit Graphics, and then go into the Import Screens sub menu. Import your screen as normal (choose Append a new screen to add a new screen, or Replace current screen if you're updating your existing title).
Once its done, go back to the Main menu, and go to Edit General Game Data. Go down to Pick title screen.... Move the arrows until you find your title screen. Press enter, and that's it! You've changed your title screen!
If you want to update your title screen, just import the new screen over the old one (Replace current screen). The editor will remember which one is the title, so you don't have to set it again.