BYOK migration - Active/Passive Region with CRR Enabled - Best Practices

First, S3 bucket cross region replication is one-way which from source bucket to the target bucket only. If you want to switch the data I/O to the replica bucket during the migration process, you should adjust the path of the target bucket. Secondly, the DynamoDB global table is in active/active mode and also a fully managed service. Data written in any region will be asynchronized to other regions, and users do not consider his synchronization mechanism and issues. Thirdly, during the migration, if all the data is written to the primary region, there is basically no major risk, but the customer needs to choose a relatively idle time for operation, takes sufficient POC testing ,Prepares data protection and plan B. Finally, provide an blog about of dynamoDB global table , hoping to help you better understand this service.

https://aws.amazon.com/blogs/database/how-to-use-amazon-dynamodb-global-tables-to-power-multiregion-architectures/