I've been searching for this forever... By default EFI partition on Mac is 200 MB. I have a special Windows 10 image (enterprise compilation) I would like to install on the Boot Camp partition, which requires that the EFI partition be 500 MB due to the image installer boot.wim file size, which is 290 MB.
The way I tried to do this is first install MS Windows 10 image downloaded from MS website by using Boot Camp Assistant to create and prepare Windows partition, then startup from the USB drive that includes the Windows 10 Enterprise image, deploy the image on top of the Windows partition, and reboot starting up from Windows to continue installation, but because I cannot copy boot.wim file onto the EFI partition, the deployment process cannot continue.
I've been trying different methods to change EFI partition size, using
diskpart when starting up from the USB drive with the Windows image, or
diskutil when starting up from macOS.
None of which allowed me to resize the EFI partition:
diskutilI get: "File system format does not support resizing".
diskpartI get: "You may not extend OEM, ESP, or recovery partitions".
Is EFI partition resizing even possible?
Due to the fact that this is a relatively new Mac, I don't think I'll have any problem reformatting the drive for this to work, and reinstall Sierra from the Recovery Mode, if necessary (Of course if it's possible to change the partition size without losing data, that's the best solution).