- create a new textfile.txt,
- change the extention .txt to .exe, choose accept changes
- go to property in the file you wanna change the default app assocition to
- Choose the textfile.exe
- change back the extention of the textfile.exe to .txt and accept the changes.
- Now the association is broken for the original file and it is set to NO assosiation.
- Ref: https://answers.microsoft.com/en-us/windows/forum/windows_10-files/how-to-unsetremove-a-default-app-for-file-type/15f2bf57-aa96-493a-b648-c81856af5eb3