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#20
The preferred way to sysprep is from Audit Mode before any user accounts are created. Install 8.1, after the last reboot when it asks for initial user name do not type anything but instead reboot to Audit Mode with CTRL+SHIFT+F3. Sysprep, reboot to OOBE, then create your user profile. Tutorial at Eight Forums: User Profiles - Relocate to another Partition or Disk.
You must empty the D: drive first, copy your user files from each profile to external disk and format the D: drive. After sysprepping restore the backed up user files to corresponding folders on D:.
I very strongly advice against copying old appdata, especially if going from 10 to 8.1. It is a sure way to trouble. But, of course it's your computer and you do what you'd like to. I'll mark you for follow up here to get noticed whenever you post, that old appdata will cause numerous issues and you will be back needing help with them.
Kari