Apple Motion 3 - Manual (Page 333)

Chapter 4 Using the Timeline 333
Overwrite
The Overwrite option deletes the existing object, overwriting it with your new object.
If the new object is shorter than the one currently in the group, the Overwrite option
splits the duration of the existing object and deletes only the frames where the new
object appears.
Exchange
Exchange is a variant of the Overwrite option, but instead of dropping the entire
duration of the new object into the project, the duration of the existing object is used.
For example, if you drag a 30-second clip over a 5-second clip, choosing Exchange
swaps the existing 5 seconds with the first 5 seconds of the longer clip.
Similarly, if you try to exchange a 10-second clip with one that lasts only 5 seconds, the
first 5 seconds are replaced, and the remaining 5 seconds would remain. The Exchange
option transfers any filters, behaviors, and keyframes from the original object onto the
new object.
Note: You cannot use Exchange with audio files.
Before After
Before After
Before After