Yes, you may remove the Global Administrator role from the admin account after the project is configured. Note, If Domain Move Migration is in-scope of the project, the Global Administrator role must be added back to the account during an active domain move as it is required to remove the domain from the source tenant and add it to the target tenant.
When planning the deployment of Domain Rewrite Service we recommend the following regarding Sender Policy Framework (SPF) records:
Update your existing SPF record to include the On Demand Migration Domain Rewrite list of acceptable domains. This will prevent any hard failures when routing mail through the Rewrite Relay Service.
Include one of the following domains with your SPF record from all source and target domains participating in Domain Rewrite based on the region where your On Demand Migration Domain Rewrite project is configured.
Global Record which includes all region-specific records
On Demand region-specific records
US
Canada
EMEA
United Kingdom
Australia
Important Tip: Do not plan on utilizing the default “tenant.onmicrosoft.com” domain when deploying On Demand Migration Domain Rewrite Services. This is due to concerns regarding the external recipient domain's having SPF hard fail enabled.
Administrators can confirm if the message has been processed by Domain Rewrite Service by submitting a message trace in Microsoft 365 admin portal or review the message header.
How can administrators confirm Domain Rewrite service has been configured for my tenants?
Administrators may verify the configurations from the Microsoft 365 Exchange Online Administrator Portal.
To verify by portal, simply login to the Exchange Online Admin Portal. Then navigate to Mail Flow. Under Mail Flow you will find the rules and connectors like the ones show below.