This sample provides a script for IT pro or windows customers to quickly batch associated file extensions with application on Windows by PowerShell.

Set-AssociateFileExtensions.ps1

<#
.SYNOPSIS
"This sample provides a script for IT pro or windows customers to quickly batch associated file extensions with application 
on Windows by PowerShell."

.DESCRIPTION
"The most efficient way to change file associations is by selecting a default program. This tells Windows that you want a 
certain program to be associated with all the file types it can handle. IT pro or windows customers want to have some kinds
of batch method to automatically associate a selection of file extensions. This sample script will help to quickly batch 
the associated file extensions with application on Windows."

.PARAMETER FileExtensions
A string array of file extensions. Each extension must be prefixed with '.'

.PARAMETER OpenAppPath
Absolute path to executable.

.EXAMPLE
C:\> (New-Object Net.WebClient).DownloadString("https://gist.githubusercontent.com/marckassay/f751c4ff681657f24fe3614e00c2396f/raw/a3433e53eb8e427c5d8a8dee6a900b745b17dbf1/Set-AssociateFileExtensions.ps1") | iex
C:\> Set-AssociateFileExtensions -FileExtensions .txt,.sql -OpenAppPath "C:\Windows\System32\notepad.exe"

.NOTES
source: https://gallery.technet.microsoft.com/scriptcenter/How-to-associate-file-3898f323
#>
Function Set-AssociateFileExtensions {
    Param
    (
        [Parameter(Mandatory = $true)]
        [String[]] $FileExtensions,
        
        [Parameter(Mandatory = $true)]
        [String] $OpenAppPath
    ) 

    if (-not (Test-Path $OpenAppPath)) {
        throw "$OpenAppPath does not exist."
    }   
    foreach ($extension in $FileExtensions) {
        $fileType = (cmd /c "assoc $extension")
        $fileType = $fileType.Split("=")[-1] 
        cmd /c "ftype $fileType=""$OpenAppPath"" ""%1"""
    }
}

Hi,

assoc & ftype commands no longer works, because file type association is now protected by a secret hash in the registry ...

Here is a solution :

1. https://kolbi.cz/blog/2017/10/25/setuserfta-userchoice-hash-defeated-set-file-type-associations-per-user/

2. https://setuserfta.com

Hope this help