Hi,

Yes, we can customize the button function by updating the 'frontdesk.WelcomePage' template. Inside this template, you'll find a statement like:
<div class="btn btn-light fs-3 py-2 px-5 mt-3" t-on-click="() => props.showScreen('VisitorForm')">Check in</div>

The showScreen function accepts a string argument representing the name of the screen in the 'frontdesk_screens' category. By updating this argument, you can show the corresponding Screens. Additionally, you can create a new Screen by adding a Component
to the 'frontdesk_screens' category.
For example, if you've created a new screen named 'CustomScreen' and inherit the 'frontdesk.WelcomePage' template, and change the div like this using xpath and position as replace:
<div class="btn btn-light fs-3 py-2 px-5 mt-3" t-on-click="() => props.showScreen('CustomScreen')">Check in</div>

This will redirect to the custom page when clicked.

Hope it helps