An enhancement request has been created by our product team and is slated to be included in a future Hotfix for the software.
Meanwhile you can create a Directory Junction and redirect default folder to any local drive.
1) Stop MAGE which writes logs to the folder you are willing to redirect
2) Delete or Rename folder you will create link for
3) mklink /J "C:\ProgramData\Quest Software\Migration Agent for Exchange\UnifiedMailSync" D:\Magelog\agent1
Please note that if you are willing to redirect the whole Migration Agent for Exchange folder you have to make sure that Share has been recreated otherwise logs won't be accessible via console.
You also need to make sure that the new redirected path has read\write permissions for the agent granted.