reset one choice; not all the choices. Even if I need to use windows registry

follow up on related question

please tell me resetting just one;
not all the choices
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☠ MASQ ☠Commented:
Sorry I missed this - if you're using related questions always put the next question link in a post at the end of your last one.

In summary what you want to do is reset just one Default App Setting in Windows 10 without affecting any other defaults that you've already "tuned".  To complicate this you want to remove any settings for that app so you get prompted for the action you want to take when you activate that app.  So you can't simply switch to one of the options pre-installed by Microsoft as alternatives.

The specific setting you are looking at is the URL:Tel protocol which determies what happens when you left-click on what is interpreted as a 'phone number in a browser window.

Unfortunately this isn't as simple as pointing at the URL:Tel entry in the registry and removing whichever default you have chosen (in this case Skype) and it reverts to its unset format prompting you everytime you click.

You'll need to do this through DSIM and that's more complex and just to make things more tricky Microsoft pushed at least three updates in the last few weeks that currently break your ability to do this (if you'd asked in January this would have worked first time!)

The way this works is you need to set up a PC with the default settings you want to use.  These may differ from the defaults Microsoft set on installation of the operating system.  Once you're happy with those defaults you export them as an xml file using DSIM.  If you then want to programatically reset one or more of those you delete just the line in the XML file relating to that app (or protocol) and then reimport the whole file with DSIM.

The important bit to understand is you can't change one setting in isolation you must import all the other settings at the same time or they will be set to Unset as well.

Microsoft have a built-in safeguard for your core associations to deal with this.

In the event you picked up some nasty infection that tried to mess with your file associations Microsoft has a failsafe in Windows 10 which checks a core selection of applications and ensures that Microsoft's default choice is set as the current option.  If it isn't then it is reset and you get a warning message that something has attempted to change your system settings.

If you just reimport your new setting for URL:Tel for example as one line of DSIM xml code you will get a few dozen warnings and all your core programs will be reset.

If you want to see the preset default from Microsoft you can run the following at an elevated command prompt
Dism /Online /get-DefaultAppAssociations >C:\TEMP\DefaultApps.txt
The output file lists all the core defaults.

If you have a system that hasn't been built or updated since end of January you can output your current settings by using
dism /online /Export-DefaultAppAssociations:"C:\Temp\FileAssociations.xml"
If you get an error message you have either a recent build or updates that currently block this (KB4058258, KB4074588, KB4088776 & KB4090914).

If you're unaffected (or once Microsoft fix the broken setting) you can then edit the xml file and reimport using:
dism /online /Import-DefaultAppAssociations:"C:\Temp\FileAssociations.xml"

If you mess up(!)
Dism.exe /Online /Remove-DefaultAppAssociations is the programattic equivalent of hitting the Reset button in Default App Settings that I mentioned in your linked Question.

It's a lot of work, you might feel that you can live with the settings you have!

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rgb192Author Commented:
complete answer that tells me in detail that it is better to remove current settings

Thank you
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