I couldn't find anywhere in user manual how to rename gates in multi gate part? You can try to change the gate name when the part is used in the schematic where in the properties dialog is editable, however, you cannot close the dialog due to error stating that a gate with the new name doesn't exist in the part. How do I rename a gate from the auto-generated a,b,c,d... to something more meaningful? It is rather difficult to use the part without this ability. E.g., if I have multiple SPIs or CAN or other ports, I have to look at the part pin assignment to see which one I want to use. Instead of just something like SPI1, SPI2 etc.
Gates are defined by a letter, that is the way it works. You can change the letter in properties as one way of swapping one gate in the package with another of similar pin quantity. The Component Bin will graphically show you the form of the gates available, so that you can choose.