Here's what I did:

1) Selected a group of ramp-down effects.
2) Right-Click, Modify This Effect
3) Check the Level Radio Button
4) Check the Change Type Box. All other "Change Effect Parameter" boxes were unchecked.
5) Clicked on OK

As expected, all effects in the selection box were changed from ramp-down to level.

BUT, all effects in the selection box were also shortened to 10 cells, which happened to be the value in the Length of Effect box in the Modify Effect dialog.

This can be a really big deal if you're changing a large number of effects and they all get shorted (or worse, lengthened to where they overlap).