Just finished installed Ubuntu as a Windows 10, Hyper-V guest.  I went to modify the video settings and noticed them to be locked in place.  After some searching; Thank you Google… Found the solution that worked for me.

Ref: Ben Armstrong’s Virtualization Blog

Steps to change screen resolution:

  1. Open Terminal
  2. Type: sudo nano /etc/default/grub
  3. Find the line starting with GRUB_CMDLINE_LINUX_DEFAULT, and add video=hyperv_fb:[the resolution you want]. The resolution I want is 1280×720. So my line ends up looking like this: GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash video=hyperv_fb:1280×720″
  4. Write the changes (Ctrl X)
  5. Run: sudo update-grub
  6. Reboot the virtual machine

When you return from your restart you will have the resolution you applied in the grub config.