How to set properties in CustomSecurity user

How can I set additional properties in the CustomSecurity field of a RDMUser object?

This field contains a xml string. Do I have to edit this myself?
What values can be set using CustomSecurity?




<?xml version="1.0"?>
<CustomSecurity>
<CanExport>false</CanExport>
<CanImport>false</CanImport>
<CustomRoles>
<string>aa259670-dae5-42b0-b3cb-4c4edd283ddd</string>
<string>6384f8e4-18fc-4239-8b24-c2e0749f1bb8</string>
</CustomRoles>
<DenyAddInRoot>true</DenyAddInRoot>
<IntegratedSecurity>true</IntegratedSecurity>
</CustomSecurity>