Hello,
Is it possible to customize the ribbon in ArcGIS Pro with our own GeoProcessing tools and if so how can we do that?
To complicate the matter further a portion of the tool is in a ModelBuilder tool and another is in a Python Script so I would need to first figure out how to combine those tools together so they appear as a single tool to the end user.
In addition, is it possible to add the custom tool to a single ArcGIS Pro project?
No. Create a toolbox and include your python script as a toolbox tool (custom tools are the simplest) and include your model there.
You can then share the toolbox with other people and/or projects.
Yes you can create buttons for your tools with the ribbons analysis gallery. I show an example of a python toolbox I have developed in my help file with links to appropriate pages here -