That is feasible. You just start the migration initially, as your initial run is completed, and the status of migration goes to not running, you go the View Progress page, and start the already configured migration.
This will pick the newly added changes, that were done to the on-premise instance, after the actual migration started.
Note: You will get a process vs total revision count mismatch in status page in such cases, as total count is not calculated only once at start of the migration.
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solved Migrating on-premise TFS 2012 to VSO with free opshub tool