What's That Flat?

Altered state

A two-letter state abbreviation is replaced by another. Examples: spa sky ; provide provoke . (Answer keys in the form of “s-pa/ky” or “prov-id/ok-e”.)

By ; (semicolon (David Millar)) — Based on content from the Guide to the Enigma from the NPL, reused/remixed with permission. — Hosted and open-source at GitHub. — Here's everything in one document. — Here's the abridged version.