I use the VSE produce sermon footage involving usually about 50 slides, which use mostly the same properties. Is there a way to specify default values for Blend Mode, Image Offset, and Length so I don't have to manually change them 50 times? I've found This answer as a work around, but then I have to add all the slides at the beginning, and I don't always know where they go until I get to them.
Don't know why this old question went up on Twitter, but if anyone comes by, there is an add-on by Snuq(not me) to handle all the needs when creating a slideshow. Get it here: https://github.com/snuq/SnuSlideshowGenerator/blob/master/Readme.md
With current versions of Blender (2.83LTS, 2.9x) you can't set defaults for this, but you can use the ALT key:
In the VSE select all of the slides you want to have the same property. When you are about to change the property, either by clicking or typing Enter to finish typing the value in, hold the ALT key while doing it.
This works for most properties and will change the value for every selected object.