Adding custom policies - AlexFilipin/ConditionalAccess GitHub Wiki
If you are adding policies to your policy set which are not in the policy repository the displayName must start with three digit number and should respect the well known number ranges.
Admin protection
Range: 100 - 199
100 - 149: Reserved for Conditional Access as Code policy repository
150 - 199: Available for custom policies
Base protection
Range: 200 - 299
200 - 249: Reserved for Conditional Access as Code policy repository
250 - 299: Available for custom policies
Attack surface reduction
Range: 300 - 399
300 - 349: Reserved for Conditional Access as Code policy repository
350 - 399: Available for custom policies
Application protection
Range: 400 - 499
400 - 449: Reserved for Conditional Access as Code policy repository
450 - 499: Available for custom policies
Data protection
Range: 500 - 599
500 - 549: Reserved for Conditional Access as Code policy repository
550 - 599: Available for custom policies
Compliance
Range: 600 - 699
600 - 649: Reserved for Conditional Access as Code policy repository
650 - 699: Available for custom policies