Oracle SQL Statement field becomes read only

I am using Oracle Database as the Source to import Data. Data connectivity mode is set to Import. All works fine.

Later when I try to change the SQL Statement, the field becomes read only and I can't edit it anymore.  Do we know why?

I have published the report to Power BI Service? Does publishing the report to Power BI Service make the field read only ?

How can I edit it if I have to make some changes?