You can use Photoshop or Photoshop Elements or some other editing program to create those title slides. Then import them into Lightroom and add them to your slideshow.
I was only able to create a single line text when trying to edit an Identity Plate.
This is a long-standing bug in Windows LR, first reported over 4 years ago. (On Mac, Alt-Enter start a new line.) I filed a new bug report: Lightroom: Can't create multi-line identiy plates on Windows
Jim & John-
Thanks for your quick reply. Yes, it is strange that you can do multi-line text on a Mac platform, and not Windows. Hopefully, the next update on LR will have this bug fixed.
Don't forget to vote and add your opinion to the bug report (link above).