Can't add blocks to prebuilt template sections?

Is it possible to add custom blocks to a prebuilt template?

For example, I am using a prebuilt carousel template on my front page, but it only comes with one button for the entire carousel, even though my carousel has three individual slides. I need a unique button to correspond with each slide in the carousel.

I also need the button to be on top of the image, not below it. There is no way to move it on top of the image as far as I can see. 

If I build any custom section, I'm able to keep adding blocks and arranging them as I like, including multiple buttons. However, without any guidance on how to build a custom carousel from scratch (not using the prebuilt template) with a unique button attached to and sliding along with each image in a carousel, I'm not able to build my carousel as it needs to be (my non-squarespace website has this feature, so I'm surprised it's not possible on SS). 

Any tips are greatly appreciated. Thank you. 

Do you have an image of your desired layout? We can help easier