Hi,
Currently, the conversion between a Power Pivot for Excel data model and a Power BI data model is one way from Power Pivot for Excel to Power BI.
May I ask why you need to convert back to Power Pivot? Power BI training Desktop offers Power Pivot, so you can do your data modeling and measure definition there.
I’ve seen some people talk about changing the file extension to ‘.zip’, opening up the archive, removing the DATA file, putting that DATA file into a similarly renamed and unzipped Excel document in the ‘model’ folder, and then rezipping and renaming the Excel file back to ‘.xlsx’. I’ve never had luck with this.
Thank you