You can't change DPI scaling automatically because it requires you to logoff and logon.
Here's a good thread on using powershell to set the DPI registry key and toggle back and forth between two DPIs a little quicker. You still have to logoff, and the script automates that.
If you want to expand on this, here is information about reading monitor information with Powershell: https://blogs.technet.microsoft.com/heyscriptingguy/2013/10/03/use-powershell-to-discover-multi-monitor-information/
And, here is information about changing the registry key of a specific user. This will be needed because if you run your script while you are not logged on, or during startup your registry hive will not be loaded. https://www.pdq.com/blog/modifying-the-registry-of-another-user/
Combine it all together with some ingenuity and you could schedule this script to run on logoff and on computer startup. The tricky part is that you will always have to be doing a new logon to get the new settings to take effect and to me, that is the biggest drawback about this.
Now, a better solution might be to change the actual display resolution which can be done without logging off: https://blogs.technet.microsoft.com/heyscriptingguy/2010/07/07/hey-scripting-guy-how-can-i-change-my-desktop-monitor-resolution-via-windows-powershell/
A lot of programs do not function properly with a non-standard DPI, and so if you ask me, changing the display resolution is a better solution.
So there you have it. All the resources to create your new script to automate this. Now you can see if you can get anybody over at http://stackoverflow.com to help you with it. :)