Sorry, wrong question. This a well done question: How do I change time format from 4/4 to 5/4 and 4/4 again? If I change using your hint , general time format is change.
You need to have the right palette on (Windows>Clefs & signature tools) Use the 3rd tool and place the time sig change where needed. An edit windows will allow you to set the correct time. This is also true for the other tool (clef of key signature).
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