If a customer is asking to change the decimal symbol on a terminal (K8). You can do so only by using the admin account and regedit.
You can use Clock and Region settings to change the admin account but not terminal.
https://www.itechtics.com/edit-registry-settings-other-users/
Use this link but quick run through:
1. Open CMD as admin
2. run reg load HKU\<username> C:\Users\<username>\ntuser.dat
username would be terminal
3. Open regedit and navigate to HKEY_USERS, there you should see a terminal profile now
4.In said profile use the find feature and search for decimal
you should see this entry and change it to whatever symbol they want to use.
Now the software should display the correct decimal symbol on the terminal users.