Get-SPScripts : PowerShell Scripts for SharePoint: Change the content type set on files in SharePoint...

If you have to make changes to a site content type architecture, the requirement may exist to change a batch of files in a document library from one content type to another. This is usually because you either need to reclassify existing documents to a new content type or move documents to another content type so that unwanted content types can be removed from the list.
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