The Excel Gantt chart is designed to be a visual representation of your MindGenius Gantt chart at the time of export that's easily accessible to others in your organization owing to the popularity of Excel, it is not intended as a replacement or even an alternative to it.
The formulae used in the chart are there to correctly colour the cells in the chart depending on date and task type at the time of export and they may not respond correctly to changes in dates post-export. In addition, the Excel chart does not include the functionality to reschedule based on link types or constraints.
If you want to reschedule tasks you should do so within MindGenius and then export the chart to Excel again.
The Excel Gantt chart is intended to be a lightweight method of distributing your project to others who need to see it, it's not designed to be an export that allows you to carry on working with your project outwith MindGenius.
The level of configuration has therefore been kept to the very minimum; all the configuration options are chosen automatically by looking at how your chart is displayed in MindGenius and using those options to display your chart in Excel.