Letterpad can be customised to some extent. However, it does not provide a ton of options. This is because we want your blog to run on steroids, super fast. Providing too many options and plugins considerably slows your blog. It's not that we are not adding features, but we are very mindful in choosing the right features for you.
Start with customising those elements of your blog, which gives your blog an identity. Clicking on Settings and start with the General Settings.
You might want to change the logo, favicon and maybe use a banner. You might also want to change some css. For this you can change the appearance section. Keep in consideration that users might be using a light theme or a dark theme, so make sure your changes look good in either of them.