Is there any builtin-easy way to call a TransformAction directly? I want to download a yaml file from a url and I need to transform it into a json file. Of course I could setup a fake repo, add all the attributes, but it there any simple way to call a TransformationAction with an already downloaded file? Or do I really need to use a custom task?

I don't think there is a built-in way to "call" a transform action, you cannot even "call" a task action. But if that is an action by you, you could of course provide some method to call your logic on an arbitrary file.