Disabling rows in ALV

I've made an ALV report. In thst I've given the functionality of Adding a row. When I add a row, I modify the internal table & populate again the ALV. It's so because I'm making it through function modules. Now I've a requirement that when the report is populated for first time, the rows should be in display only mode. The new row inserted should only be editable. Right now every row is editable.