Yes, you can add a new variation to an existing listing that is already published on your Etsy store. There are two ways you can do this.
First method: Creating the variants directly from the Product Detail Page in Gelato
1. Find the product you would like to add variants to in your store and click on Edit Product > Edit Design
2. In the sidebar on the left of the Product detail page, you will be able to select the new variants (new sizes or colors, etc) and adjust the design if necessary.
3. Publish the changes
Note: For this to work, the product must be created from the Gelato Dashboard. All variants must be connected and not ignored. Additionally, all variants must be connected to the same product type. This means it will not work if one or more variants are not of the same type (eg. Some variants are posters with frames, some are posters with hangers, and some are posters without frames).
Second method: Create the variant in Etsy and connect it in Gelato
1. Create the new product variation manually in Etsy - see the example below.
Open your listing in the Etsy Shop Manager and click on "Edit variations"
Create a new variation, e.g. "Frame" and click on "Add".
Create some options for the newly created variation, e.g. "No frame" and "Black frame".
A new variation will be created.
2. Please go to Gelato Dashboard and in the section 'Stores', enter the store page with all products and click on "Sync products" (the button is located on the top right corner of the page). After a while, you will see a new variant as "Not connected".
3. Connect the new variation to Gelato as shown here.
Note: If there will be a price difference between the variants it is very important to check the box "Prices vary for each XXX" (For example "Prices vary for each size") or the new product won't connect to Gelato.