RE: If 200 test cases are prepared and out of that 50 ...
Given the timelines find out the priority of the 50 modified conditions. High priority conditions based on the business/user needs are always treated foremost and those conditions are executed. Logically all the 200 conditions need to be tested to ensure test coverage. But if there is a constraint of time the high priority conditions are executed first with the rest un-tested conditions mentioned in the test report along with suitable explanation.