Migrating players’ data or Leaderboard is not supported, but there are workarounds.
Since the Master Player Account is shared between titles within the same studio and Player Data (Publisher) can be shared between titles. My suggestions is that using Scheduled Task with Cloud Script to transfer Statistics to Player Internal Data (Publisher). When the player uses the same identity to log into new account, you may create a restore function in Cloud Script, which will transfer the data in Player Internal Data (Publisher) to Statistics, then clean Player Internal Data.
Meanwhile, if titles are in separate Studios, this cannot be done easily except there is an external database server to cache data.
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