How to open .CSV file with Microsoft Excel

The thing is - all Microsoft Office documents are ZIP files containing XML files. I would try this:

• copy the XLSX to another location
• Rename the copy by addin ".zip" to it (ignore the warnings)
• unzip the copy with your favourite tool (Unarchiver or terminal "unzip ")
• look through the folder structure and find your zip file.

For Excel V15, use a posix path, like this:

set theOutputPath to POSIX path of ((path to desktop folder as string) & "My Saved Workbook.csv")
tell application "Microsoft Excel"
    tell active workbook
        save workbook as filename theOutputPath file format CSV Mac file format with overwrite
    end tell
end tell

Edit 1 -

I test it on V15.15 and V15.16, it's a bug when the destination folder doesn't contains a recently opened Excel file. So use it

set theOutputPath to POSIX path of ((path to desktop folder as string) & "My Saved Workbook.csv")
set parentFolder to (do shell script "dirname " & quoted form of theOutputPath) as POSIX file -- get the parent folder 

tell application "Microsoft Excel"
    alias parentFolder -- a folder where to save a new file, workaround to a bug when the destination folder doesn't contains a recently opened Excel file
    save workbook as active workbook filename (theOutputPath) file format CSV Mac file format with overwrite
end tell

Edit 2 -

Or create an empty file like this

set theOutputPath to POSIX path of (path to desktop folder as string) & "My Saved Workbook.csv"
do shell script "touch " & quoted form of theOutputPath -- create an empty file
set theOutputPath to theOutputPath as POSIX file
tell application "Microsoft Excel"
    save workbook as active workbook filename (theOutputPath) file format CSV Mac file format with overwrite
end tell

Edit 3 : I had another idea, it would be the simplest script.

set theOutputPath to (path to desktop folder as string) & "My Saved Workbook.csv"
tell application "Microsoft Excel"
    alias theOutputPath --  workaround to a bug when the destination folder doesn't contains a recently opened Excel file
    save workbook as active workbook filename theOutputPath file format CSV Mac file format with overwrite
end tell