There may be a registry key for this, but I don't know it.
Instead: Try making a default workbook and worksheet. Create a workbook with gridlines turned on.
Then follow Microsoft's instructions for saving this as a workbook (Book) and worksheet (Sheet):
"You can save workbook settings that you frequently use in a workbook template, and then automatically open that workbook template every time that you create a new workbook.
- Do one of the following:
- To use a workbook template, create a workbook that contains the sheets, default text (such as page headers and column and row labels), formulas, macros, styles, and other formatting that you want to use in new workbooks that will be based on the workbook template.
- To use a worksheet template, create a workbook that contains one worksheet. On the worksheet, include the formatting, styles, text, and other information that you want to appear on all new worksheets that will be based on the worksheet template. Settings that you can save in a workbook or worksheet template
- Cell and sheet formats.
- Page formats and print area settings for each sheet.
- Cell styles.
- The number and type of sheets in a workbook.
- Protected and hidden areas of the workbook. You can hide sheets, rows, and columns and prevent changes to worksheet cells.
- Text you want to repeat, such as page headers and row and column labels.
- Data, graphics, formulas, charts, and other information.
- Data validation settings.
- Macros, hyperlinks, and ActiveX controls on forms.
- Workbook calculation options and window view options.
- Click File > Save As.
- In the Save as type box, click Template.
- In the Save in box, select the folder where you want to store the template.
- To create the default workbook template or default worksheet template, select either the XLStart folder or the alternate startup folder. To find out the path of the startup folder, see Locate the XLStart folder.
- In the File name box, do one of the following:
- To create the default workbook template, type Book.
- To create the default worksheet template, type Sheet.
- Click Save.
- Click File > Close."