Editing Material Functions
At times, you may need to change the functionality of a material function. This can be done directly from the Content Browser, or from within a material utilizing the given function.
In either the Content Browser or the Material Editor's Graph tab, you can double-click on a material function to open it up within a separate Material Editor tab and see the network of material expressions that make it up. In this way, the internal network of a material function can be edited and updated at any time.
However, it is important to note that any changes made and saved to a material function will be present in all instances of that material function moving forward. For example, if you made a change to the internal network of a Radial Gradient material function, all existing instances of that function would receive the update, as well as all new instances moving forward.
For this reason, unless you are certain that your change needs to propagate throughout all other instances of the function, it may be wise to make a copy of an existing function in the Content Browser (right-click and choose Duplicate from the context menu) rather than editing the original material function.
Once you make changes to a function you have to click the button to propagate the changes to the function asset and any materials using the function. Once done, be sure to save your asset in the Content Browser!