I'm new to shopify and I'm trying to figure out how to build public app that will be able to update store UI
For instance, I need to replace add to card button to my custom button that will change behaviour or I want to add some button / html somewhere.
So my question is how can I do that as aplication developer? I've checked app bridge and polaris but that looks to be useful for admin part only
Sounds like you are looking for the Script Tag API: