The POTUS would not have revised these exercise plans unless the ROKs were in full coordination and agreement
Yeah, well it's pretty clear from early reports that the South Koreans weren't aware Trump was going to do this.
Here's a link to the Chosun-Ilbo English language coverage. Money quote is here: "...Trump then managed to alarm South Koreans with a throwaway promise to end "war games" with South Korea, which he called "very expensive" and "very provocative."
Surprise!