I received a requirement to be able to customize Opportunity Close entity to change/edit Status reasons to include some specific reasons.
Using my instance, I was able to make changes/edit the status reason for Opportunities Close entity.
STEP 1
1. In the Dynamics 365 Sales application, click on Settings
2. Click on Customization
3. Click on Customize the system
4. In the Solutions Explorer, expand the entities, scroll down to "Opportunity"
5. Expand the Opportunity entity and click on Fields
6. Search and double click to open "Statuscode" with display name "Status Reason"
7. Change the status field to "Lost"
8. Click on add
9. In the "Add List Value" box, type label and copy the Value number, in this case Label: TestLost and Value: 756,150,002
10. Click on Save and close
11. Publish the Opportunity entity
STEP 2
1. In the Solutions explorer, expand the entities, scroll down to "Opportunity Close" entity
2. Expand the Opportunity Close entity and click on Fields
3. Search and double click to open "opportunitystatuscode" with display name "Status Reason"
4. In the Options, click on + icon to add the specific reason in this case Label: TestLost and Value: 756,150,002 (past value copied in the number 9 of Step 1 above)
5. Save and Close
6. Publish the Opportunity Close entity.
7. In the Unified Interface, open a Opportunity record, click on Close as Lost
For further information please visit documentation on https://docs.microsoft.com/en-us/dynamics365/sales-enterprise/customize-opportunity-close-experience
The above steps works fine in my environment.