Professional :: Pasting Into Successive Keyframes?

I like to keep my timelines compact, so I often have several graphics in a single layer. Let's imagine that I have a series of five keyframes, with four shapes in each one. Over the course of those five keyframes, one of the four shapes changes into a different shape. Now, let's say that I realize that one of the static shapes needs to be something different. "Oh no! That circle shoudl be a triangle instead!".
 
I know how to use Edit Multiple Frames to drag a box around that shape and delete it across those keyframes, but there are a few problems with that.One is that if the keyframes are really long or I have more like 30 or 40 keyframes in which I want to make this change, I have to drag and scroll and drag and scroll the shaded part of the playhead to cover all the of the keyframes or be willing to do it in chunks. Also, if the thing I want to delete is sitting on top of something else,then I can't drag a box around it without selecting that other thing. I could click the object and delete it, but that only deletes it from the right-most keyframe. I then have to click and delete for every keyframe.
 
All of this is secondary to the fact that Edit Multiple Frames doesn't seem to allow you to paste something into all of those frames. At least, not any way I can tell. I suppose this is a sade-effect of not assigning every asset its own layer, but that would get almost unmanageable with some of the projects I work on.if there's a way to paste things into multiple/successive keyframes on the same layer?