You may use the solution in this page.
For simplicity here are the steps;
1. On any windows 10 computer set the defaults that you would like to use via GUI.
Settings > Apps > Default apps
Defaults Apps Window
2. Run the following command on cmd.exe to export XML template based on currently selected defaults:
Dism.exe /online /Export-DefaultAppAssociations:C:\DefaultApps.xml
3. Copy the created XML file to a shared folder (if you want to change the defaults apps and automatically reflected on the other machines) or just move by a USB stick and then point this in Group Policy Settings on each machine.
Computer Configuration > Administrative Templates > Windows Components > File Explorer > Set a default associations configuration file
Select Enabled and input the XML file location
Set a default associations configuration file
4. To make them not change the settings you should not give its accounts the admin rights.