Hi Roberto,
Thanks for your interest in syncfusion products.
We regret to let you know that currently we don't have support for customizing the text properties in MessageBoxAdv.We will implement this feature in our forthcoming new version releases or service pack releases. The feature implementation would also greatly depend on the factors such as product design, code compatibility and complexity. We will get back to you once the feature is implemented.
Please let us know if you have any concerns.
Regards,
Paul Anderson S