Is a new rule where debt-to-income ratio impacts your interest rate a local rule or a nationwide change?

Nationwide. Mortgage pricing rules are set at the agency level, and what you heard describes Fannie Mae and Freddie Mac's national LLPA grid, not a Vegas rule. Loan-level price adjustments are the pricing framework Fannie and Freddie apply to conventional loans, and they work the same in every city and state. The change people talked about reworked the credit-score tiers. The top tier that once opened at 740 moved higher, so some borrowers in the 740 to 779 range pay a bit more than before, while some lower-score borrowers in the low-to-mid 600s saw reduced adjustments, effectively subsidized by the higher-score group. A separate DTI-based price adjustment was proposed around the same time and scrapped before it ever took effect, which is probably where the rate-tied-to-DTI version of the story came from. Tiers and adjustments change over time, so confirm the current grid when you price a loan. The stated rationale was promoting equity, and skepticism there is fair: LLPAs were built to price the actual default risk Fannie and Freddie guarantee, and a credit score reflects payment history rather than any protected characteristic. Whatever you make of the policy, the practical takeaway is unchanged. A stronger score earns better pricing, so put your effort there.