How to share fields between commerce variation types? Assume I have more than 100  different variation products and all of them share same fields ( such as commission rate, Brand, Weight and etc). As I understood so far, I need to create 100 product variation first. 

Now, my question is:

Do I need to add each of these fields for each variation separately? or is there any way to add them only one? e.g how can I add these fields to the product entity so that every time I create a variation, it automatically adds all these fields, similar to sku and price?

p.s: I use commerce_kickstart-7.x-2.40

Any help will be highly appreciated!

Thanks
It sounds like what you're wanting to do is create a group of product variations where you only have to specifically set the unique field value per variation. If that's the case, it isn't possible. We tried to implement some sort of field inheritance model where you could set default field values for each variation at the product display level, but it never developed.

The closest thing is the Bulk Product Creation module, which does let you create a whole set of related product variations at once. I don't believe it's been integrated into Inline Entity Form / Kickstart 2.x, though, so you may want to play with it first in a development environment before trying it in your live database.