Custom Square Code Modification

I need custom code for Square to modify sale processes. Specifically, I want to change modifier behavior so that a modifier is only charged once per transaction, regardless of item count.

Key Requirements:
- Ability to modify sale processes in Square
- Change modifier charging behavior
- Apply to apply change to just desired item pages not all items.

Ideal Skills & Experience:
- Experience with Square and its APIs
- Strong coding skills, especially in payment processing systems
- Familiarity with transaction modification

I am looking for someone who can efficiently implement this change and ensure it works seamlessly within the existing Square framework.