What rule should I check first?
Read the applicable local patent rule and case order. For example, Northern District of California Patent Local Rule 3-6 permits amendment only by court order upon a timely showing of good cause. Its examples address unexpected claim construction and newly discovered material despite diligence; the rule also considers prejudice. Those examples do not create automatic permission.
What should a request explain?
Identify what changed, when it was discovered, the efforts made earlier, why amendment is needed, and the effect on the other side and schedule. Rule 16(b)(4) requires good cause and judicial consent to modify a scheduling order. Address both the local disclosure rule and the schedule if both are implicated.
Why not keep a fallback theory in reserve?
An amendment request should be built on the governing standard and a documented timeline. A preference for a different theory later does not by itself establish diligence or good cause. Treat initial claim and product disclosures as substantive work rather than a placeholder for unrestricted revisions.