Add variations to coupons commerce module of drupal
Sure, no problem. Just create a new rule that triggers on the event "Calculating the sell price of a product."

You want the condition: Entity has field, then choose the commerce_product. This is the product reference field that is inherent in line items.
Then, choose the condition: Entity has field again. Choose the brand entity reference field that you have built into your product type. Basically, you will be reaching through the line item, through the product the line item refers to, to hit the brand that product is tagged with.
Next, choose the condition: Data comparison. For Data to Compare, choose that brand reference field. For Data value, switch from data selection to direct input mode, then choose the brand you wish to target.

Finally, under actions, add one of the commerce line item actions based on the mathematical operation you wish to do with that brand price. 

This should do it!