Great question. In Odoo (Release 18), once you’ve created individual products (A, B, and C) as standalone items, you cannot directly convert them into variants of a single parent product without reconfiguring their structure. Variants in Odoo are generated based on product attributes (like Size, Color, etc.), and the system treats standalone products and product variants differently at the database level.

If you want A, B, and C to become variants under one parent product, you’ll need to:

1. Create a new parent product configured with attributes and values (e.g., Attribute = Model; Values = A, B, C).
2. Recreate or migrate the existing data (costs, images, descriptions) into the variants manually or via script/API.
3. Deactivate or archive the original standalone products to avoid duplicates and confusion.

Regarding costs, images, and descriptions:

• Each variant can have its own cost and image.
• Descriptions (sales/purchase) can be inherited from the parent or customized per variant.

Let me know if you need help with the best approach or automation to simplify the transition.