Thank you for reaching out to us. As I understand you want to customize Information Protection Label fonts.
Any example/screenshot that you can share, which particular setting/value you want to customize.
Below are few articles which refers to customization
https://learn.microsoft.com/en-us/azure/information-protection/rms-client/clientv2-admin-guide-customizations#specify-a-color-for-the-label
https://learn.microsoft.com/en-us/azure/information-protection/configure-policy-migrate-labels#:~:text=Custom%20font%20name%2C%20size%2C%20and%20custom%20font%20color%20by%20RGB%20code%20for%20visual%20markings%20(header%2C%20footer%2C%20watermark)
Let me know if you have any further questions.