How to push a file sometimes but always pull it

I created a project and for demonstration purposes, i need to have some static files (like a database or images) in the project. I mean, to test the application, the database can be changed (it’s a simply .db file) and also some pictures can be removed.

When my test are ok, then i push on a branch the changes.

1) When i push the changes i want to decide if this specific files (data.db, picture.jpeg for example) must be push or not. (I may need to update them or not)

2) When i pull the branch i want always these files to be taken from the branch and replace the same file i have locally.

Can anyone help me?