Answer
- There are no out-of-the box API calls available to do this. The only way we know that it could be done is using OpenXML commands, but this would not be supported.
- There are pending enhancement requests to add this as a supported API.
- One short term solution might be to generate a CSV file instead, with the first line being “set=comma” with an XLS extension. This would make the CSV file opened as an Excel file with the proper delimiter, regardless of regional settings.
Source: Office Hours 2020-09-27 Partner Enablement