Editing Coordinate Reference Systems
To edit an existing CRS properties, hover over it with the mouse,

A native CRS (one attached to the model when it was imported) can be edited but it cannot be deleted - see below for a user-defined CRS.

The CRS may be deleted, edited or locked/unlocked. A locked CRS may not be edited or deleted
To create a CRS transform between 2 CRSs click and drag the mouse between the left/right nodes on each CRS:
The Following Native CRS has been linked to 2 other user defined CRSs and 2 CRS transforms created

To edit the transform between 2 CRSs hover over the 'i' symbol:

The icons are, respectively, left to right: Edit, Delete or Lock/Unlock
A locked transform may not be edited or deleted
Hover over the edit icon to see a preview of the transform steps:

Click on the icon to edit the transform