Pending Oct 1 Direct Bill requirement changes.

I don't fully understand the statement from Microsoft here, regarding needing to move or rebuild resources. As changing from CSP Direct Bill towards a CSP Indirect Reseller status (via a CSP Distributor) is a very simple process.

Your new CSP Distributor can simply submit a CSP Transfer Request towards you as a CSP Direct Bill partner, and you approve the request and done (now the Azure is transacted thru Indirect channel)! No downtime, no rebuild required. All resources are transferred 1:1 towards the CSP Distributor as the new billing account.  

Do note that the CSP Distributor should be add a Foreign Principle to the Azure Subscriptions to ensure PEC. 

If you mean changing a customer's Azure Subscription from EA contract towards CSP, then yes, that's a hassle. Only a few dedicated partners can support with that for transitioning EA towards CSP (I believe only Azure Expert MSPs get the required tooling for this). Otherwise it's rebuild indeed. 

This is due to EA Azure actually being part of a different/legacy Azure platform, while CSP Azure is on the modern Azure platform.