changing value of custom property via script

Sure. Setting custom properties using a script is a common task. You can get started here: https://github.com/solarwinds/OrionSDK/wiki

If PowerShell is a good scripting language for you, here's a sample showing how to set a custom property value: https://github.com/solarwinds/OrionSDK/blob/master/Samples/PowerShell/CRUD.SettingCustomProperty.ps1

So where do you get the SolarWinds powershell module from?  There is a link for the SDK, but nothing for PowerShell that I can find via that link other than some scripts.  I appreciate your help but I don't think this should be marked as the correct answer.

It looks like the powershell module is installed with the beta version of the sdk.

Yes, version 2.5 of the SDK will take care of installing the module for you. You can either install that beta (maybe you already have) or use the method at the top of https://github.com/solarwinds/OrionSDK/wiki/PowerShell

> To install this module from the PowerShell Gallery, use Install-Module -Name SwisPowerShell. You'll need to be running PowerShell as an administrator.