Repro Steps:
1. Assign a Shadergraph to a material
2. Change an Enum Entry Name (Suffix), Save Shadergraph
3. Change Enum Reference, Save Shadergraph
4. On the Material, change the Enum that's currently selected to any other option.
5. Change your inspector to Debug Mode, observe the Shader Keywords field.

Actual Results:
Shader Keyword would be replaced with the new reference prefix+suffix combo

Expected Results:
Shader Keyword is appended with the new reference prefix+suffix combo

Additional Note:
After reproducing the issue, observe the SavedProperties Field. Notice that the old Keyword reference name is still present within the float list. This may or may not be related to this issue.

Reproduced on:
Editor 2019.3.2f1, Shadergraph v7.1.8
Editor 2020.1.0a23, Shadergraph v9.0.0