One of the biggest automated migration issues was always the fact that many companies have Windows 7 x64 in place but due to legacy issues with UEFI deployments in the past they stick still with LEGACY Bios settings and not with modern and much more secure UEFI boot bios settings. UEFI also need GPT partitioning and not MBR partitioning.
To remove this hurdle Microsoft introduced in SCCM 1610 a nice feature that allows you to migrate to UEFI during a task sequence.
Additionally to the task sequence you may need a vendor specific tool that allow you to migrate your bios settings to UEFI.
More you can find here:
https://docs.microsoft.com/en-us/sccm/osd/deploy-use/task-sequence-steps-to-manage-bios-to-uefi-conversion
Example with Dell CCTK.
The original blog still refer to an older alternate way. But the rest of the article in the end refer to the Dell CCTK tool to modify the BIOS. This is still valid.
http://www.scconfigmgr.com/2016/06/14/switch-from-bios-to-uefi-on-dell-systems-during-windows-10-deployment-with-configmgr/
Enjoy the show!