Yes. With Cellesim you top up the eSIM you already installed. You do not scan a new QR code, you do not install a second profile, and your phone number setup does not change.
Open the Cellesim app or your account page, pick a top-up for the eSIM you are using, and the data is added to the same line. The validity period is extended at the same time, so a 7-day plan topped up on day 5 keeps running instead of expiring.
This matters most when you are already travelling: running out of data usually means you have no connection to buy more with. Because the top-up lands on the existing profile, it works as soon as it is processed, without Wi-Fi and without reinstalling anything.