Play by the Rules Act of 2019 This bill subjects certain merchandise from a nonmarket economy country (a foreign country that does not operate on market principles of cost or pricing structures) to existing antidumping or countervailing duty orders. The Department of Commerce shall include any merchandise from a nonmarket economy country that is only slightly altered in form or appearance within the class or kind of merchandise that is already subject to (1) an investigation, (2) an antidumping duty order, (3) a finding under the Antidumping Act of 1921, or (4) a countervailing duty order. Additionally, Commerce may include within the scope of an investigation, order, or finding any merchandise from a nonmarket economy country that is (1) slightly altered in form or appearance but was not previously included within the scope of such investigation, order, or finding; or (2) interchangeable with imports that are already subject to such investigation, order, or finding.