How can a CSP customer with active subscriptions correct an incorrectly recorded billing country from SG to MY?

Question

We are a CSP partner assisting an existing Malaysian organization.

The customer’s registered business operations and billing address are in Malaysia. However, the Partner Center Customer Billing Profile is currently recorded as:

{ 
"culture": "en-SG", 
"language": "en", 
"defaultAddress": { "country": "SG" } 
}

The remaining billing-address information in the profile, including the city and state, reflects a Malaysian address. We are therefore trying to determine whether this can be treated as a correction of an incorrectly recorded country rather than a normal relocation from Singapore to Malaysia.

The customer already has active Microsoft 365 subscriptions, assigned licenses, users, custom domains, mailboxes, and production service data.

As an initial test, we attempted to change only the billing-profile culture from en-SG to en-US, while keeping the country as SG, through:

PUT /v1/customers/{customerTenantId}/profiles/billing

Partner Center returned:

{ 
"code": 600078, 
"errorName": "UnableCustomerOrganizationOrCulture", 
"message": "Not allowed to update customer culture or language, please work with customer to update.",
"isRetryable": false 
}

The customer’s Global Administrator also checked:

Microsoft 365 Admin Center 
→ Settings 
→ Org settings 
→ Organization profile 
→ Organization information 
→ Preferred language

However, the only available value is the generic option English. There is no option to select en-US, en-SG, or en-MY.

Microsoft Support previously advised that the billing country of an active tenant cannot be changed directly and recommended creating a new Malaysian tenant. However, the customer already has active subscriptions and production data, and the physical and billing address has always been in Malaysia.

Could someone clarify the officially supported process for this situation?

1. Can Microsoft correct the existing Customer Billing Profile country from SG to MY through backend support when the current country appears to have been recorded incorrectly?
2. Is there any customer-controlled interface that can update the exact billing-profile culture from en-SG to en-US or en-MY?
3. If a new Malaysian tenant is required, can the existing CSP subscriptions be migrated or transferred to it?
4. Will the current subscription terms, quantities, commitment and renewal dates, pricing, and license assignments be preserved?
5. Is cancellation and repurchase required, and could this result in early-termination charges or duplicate billing?
6. How should existing users, custom domains, mailboxes, and Microsoft 365 service data be migrated?
7. Can the current Singapore-country tenant remain operational while the new Malaysian tenant is prepared and validated?
8. What downtime, data-migration risks, or service interruption should be expected?
9. Is there an official Microsoft procedure or documentation for correcting an incorrectly recorded tenant country when the customer already has active CSP subscriptions?

We are specifically looking for guidance applicable to an existing Malaysian CSP customer with active subscriptions and production data, rather than instructions for creating a new customer with no existing services.

For privacy, customer identifiers, domain names, contact details, tenant IDs, subscription IDs, request IDs, and address details have been omitted.