How to insert a minion Powershell variable into Salt Pillar or Mine? Say I have a Powershell script, named test.ps1, that has this:

$VariableForPillar = 5 


I can call it from a Salt state with -

test powershell run:
 cmd.run:
   - name: 'C:\Windows\System32\WindowsPowershell\v1.0\powershell.exe  -ExecutionPolicy ByPass -File  d:/tmp/Powershell/test.ps1'


But what can I do to retrieve that value and insert it into a Pillar (or a Mine)?
You can only insert the return into the mine.

Just specify the cmd.run (or possibly cmd.script) in your mine_functions and you will get the whole return back.

If you want to have a script that sets up extra config on the minion, I would recommend writing a custom grain.

https://docs.saltstack.com/en/latest/topics/grains/#writing-grains