In the vast majority of cases, No.
Polaris has been designed so that your customizations overlay NOT replace standard Polaris files. That means when we deliver new files with an upgrade, your customizations don’t get overwritten as part of the process.
Customers who have done extreme customizations often choose to make modifications to Polaris-defined pages. In those cases, the customer documents the changes they make and re-apply them after an upgrade. This level of customization is very rare.