Hi,
Region drawing was enabled for load CXR since 02-28 DB, it is in Corona 12 Update 2 as well:
https://forum.corona-renderer.com/ Chaos Corona 13 for 3ds Max - Daily Builds Changelog #msg231652
VFB - Region draw is enabled when editing CXR, but only when edited CXR is of the same size as current/last rendering, which is necessary for resume render.