Question How to auto add keys at first frame when pasting keys from different clip?

Hello, I've been scratching my head over this for a while, and I can't seem to find an answer anywhere.

I'm trying to manually create animations that act as transitions between other animations. For example, an animation that bridges a walk loop and an attack loop so they transition seamlessly. I'm using 2D bone rigs, and automatic transitioning creates many visual issues with my rigs, so I'd rather animate it manually.

The issue is how difficult it is to create those animations. I'm trying to transition from walk to attack, but when I paste my attack keyframe (which animates more parts), it messes up my walk keyframe. Here's an example of what it looks like in the timeline:



Every frame the attack animates that the walk doesn't messes up the walk pose. If Unity could automatically add keyframes at the start when I paste something that would solve my issue. Of course, I can manually adjust/reset every affected frame, but this takes a really long time.

Any help is greatly appreciated, thank you.