Ctrl+Delete of the first measure does not normally delete the time signature, and even if you actually choose to delete the time signature (by selecting it rather than the measure when deleting), it is usually simple to add it back. If you have a particular where this is not working as expected, please attach it so we can investigate.
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copy/paste 2nd to 1st measure, then delete 2nd measure
Ctrl+Delete of the first measure does not normally delete the time signature, and even if you actually choose to delete the time signature (by selecting it rather than the measure when deleting), it is usually simple to add it back. If you have a particular where this is not working as expected, please attach it so we can investigate.