Yes, the entries in the External Reference column can be edited through individual responses.
Please follow the steps below:
1. Go to Analytics > Responses > Response Viewer
2. Click on the relevant Response ID
3. Select Edit Response
Here’s a screenshot for reference: https://prnt.sc/D8B2u6cXAg_F
Please refer this helpfile for more details: https://www.questionpro.com/help/response-viewer.html
Can I add custom1 + custom2 and show the value?
Is it possible to go above the 255 threshold (more like 300-500).