Thanks, but I think you gave me the tip I needed already!
For those stumbling here through google with the same question: my scope was altering/hiding some steps and adding several others, for a customer with a very extended product. Ie: their prices are generated from a formula based on various parameters, so the price tab "existing" could lead to accidental overwriting. MANY, MANY new switches and fields.
"displayAdminProductsExtra" is too hidden away, we aimed at more visual clarity for the client's large team.
On top of Knacky's suggestion, I'm attempting to override 'PrestaShopBundle\Controller\Admin\ProductController' from the module's 'config/services.xml' file. From there I should be able to:
- override createFormBuilder() to add my data/steps
- change the main template through the @Template annotation of formAction() if needed
- use Knacky's method to improve the other tabs
\o/ Good luck.