If i change my sales cloud instance from NA30 to NA82 or some other instance so do i need to reinstall MC connector again ?
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Instance change only affects your integration if the ORG ID is changing. If your ORG ID remains the same, then there is nothing required from your end to have your integration with the Marketing Cloud to continue working.
You might find more information here: https://help.salesforce.com/articleView?id=Instance-Refresh-Maintenance-FAQ&type=1&language=en_US