I want to make sure I'm understanding you @konrad.
Do you mean that you would like to adjust the price of a modifier conditioned to whether this is to add or substitute? Example sub-American for cheddar cheese is free but adding cheddar cheese is 0.79 cents)?
If understood correctly then this would be considered a feature request and you can submit it here. This will help our product team get visibility and track other Sellers with similar interest in your request.
Important: When submitting a request, make sure to include the desired feature, and provide the details of how this feature will help your business succeed (how would you use it and what you expect from it).
In the meantime, you can create modifiers for individual actions. While this isn't convenient at all it would solve your issue. You would create an Add Cheddar Cheese and the price and a Sub Cheddar Cheese with no price increase.
I hope this information is helpful and Welcome to the Seller Community!
JJ
Community Moderator, Square
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