No you wouldn’t. You could just have multiple assigns inside the For Each Row loop.
Assign row.Item(0) = Left(row.Item(0).ToString,100)
Assign row.Item(1) = Left(row.Item(1).ToString,100)
…etc
Of course, it would mean less code if you did do a For Each inside the For Each Row.
The expression on the left is CurrentRow.Item(columnName)