Of course I opened an OSS message to SAP.
My previous plan was not complete ... I wanted to say that I want to:
- Drop the index
- Proceed with the upgrade
- After the upgrade is finished, I will revert back the field definition to 180 instead of 3999
- Recreate the index
Even though this will work, I still need a solution from SAP because I am not planning to do that in production.