Workflows can automatically assign categories when certain criteria are met. To find more information related to creating workflows, see the workflow knowledge base section.
Workflows give you the ability to add conditions to be met prior to assigning categories to products.
When assigning categories through workflows, new categories can either be added to products with existing categories or overwrite existing categories. To add categories rather than overwrite, choose the 'Extend the current categorisation instead of replacing it' option on the dialog.
Note: If the workflow is set up to be triggered on product create, the 'Extend the current categorisation instead of replacing it' option must be selected.