I don't know of any way to rotate a Image or Texture2D node directly, but you could probably use a Viewport to achieve a similar result.
In theory all you need to do is place all of the textures as Sprite nodes that are children of a Viewport node, set the Viewport node's size to the desired size, set a Camera2D node so the contents of the Viewport are visible, and then use the Viewport output as the final product.
That way to rotate, scale, and position the sub-images, you can just change the properties of the Sprite nodes and let Godot handle manipulating the images within the Viewport.
The Viewport demos in the Godot demo repository kinda show how this could be done. There is also this page on the documentation that uses a Viewport as a texture for a procedural planet, which might help as a reference.
Hopefully this helps a bit. It should totally be possible to use rotated textures, it just might require using Viewport nodes instead of rotating the image/texture directly.
(Side note: Welcome to the forums!)