No, you can't. It will import and re-export every cell, not just the one you modify. This includes interpreting dates and rounding numbers that exceed Excel's max value (instead of interpreting as a string)
They have a small banner at the top to warn about this, but it doesn't even address the things that were already lost the instant you opened it.
If you're just editing some values, you can save back to CSV with CTRL+S no problems.