Optional build-in/out in Templates?

I'm fairly new to Fusion. I did try looking online, but could not find an answer to this.

In Apple Motion, I can build a "generator" animation with optional build-in/out frames as well as the middle chunk that expands infinitely when you increase the duration of the generator in the timeline.

In Fusion, I have built a lower third title that animates in and out, but sometimes I want the middle to expand appropriately to match its underlying video clip. Also, sometimes I may want to bypass animating the lower third and just have it appear with no animation. Is this doable in Fusion? Can someone point me in the right direction?

I kept digging and found the Keyframe Stretcher Node, which solves the main problem of allowing the middle of animation to stretch infinitely.

Now I just need to see if optional build-in/out rigging is possible.