Here is a script to update all templates standard values. Just update the guid and the path to your templates.
Note that you can easily enhance this script to adapt for existing items on the content tree as well. This should get you going:

    	$templates = Get-ChildItem -Path "/sitecore/templates/My Project Templates" -Recurse | Where-Object { $_.Name -match "__Standard Values" } | ForEach-Object{
    	    $_.__Workflow = "{A5BC37E7-ED96-4C1E-8590-A26E64DB55EA}"