The procedure described by “Pig Master” above worked for me (I use Windows XP, can't confirm it for other operating systems). However, the directions are so compressed that they are difficult to follow. Also, it only shows how to associate spreadsheet files with LibreOffice.
The instructions below attempt to clarify and generalize the procedure for all common file types.
Although there are many steps listed, they are all simple and quick, don't be discouraged. (It often takes a lot of words to clearly describe a simple action.)HOW TO CHANGE FILE EXTENTIONS FOR LIBREOFFICE
WITHOUT REINSTALLING IT (WINDOWS XP)
1. Open Windows Explorer.
2. Select "Folder Options" from the Tools Menu.
3. Select "File Types".
4. Scroll through the listed file extensions to find the one you want to associate with LibreOffice. (See Notes 1 to 4 below.)
5. Select the desired file extension from the list.
6. Click the Advanced button.
7. Click the New button to open the "New Action" window,
8. Enter "open" in the "Action" field (without quotes).
9. Click in the "Application used to perform action" field.
10. Click the Browse button.
11. A window should open set at the "Program Files" folder (if it doesn't, navigate to "C:\Program Files").
12. In the list of files, find and open the LibreOffice file folder (the folder may have the version number after the name) by double-clicking on the name.
13. Open the "program" folder (double-click on the name)
14. To make it easier to find the EXE file you need, click on the View menu at the top of the window and move down to the "Arrange Icons by..." and select "Type" from the sub-menu. All the EXE files will now be listed first following the folders in the list.
15. Find the LibreOffice program you want to use to open your documents and click on it, then click the OK button. (See Note 5 below.)
16. In the "Edit File Type" window, click on the "Edit..." button.
17. Click in the "Application used to perform action:" field, and scroll to the end of entry (use the right arrow key on your keyboard).
18. Insert double-quote marks around the last two characters (Change %1 to "%1" ).
19. Click the OK button to close the window.
20. Click the OK button to close the next window.
21. Click the Close button to close the final window.
22. [Optional] In Windows Explorer, select "View" from the menu, move down to the "Arrange Icons by..." and select "Name" from the sub-menu to restore the sorting order to it's default setting.Notes to Step 4:
1. Some common LibreOffice file extensions are: Text: ODT, Spreadsheets: ODS, Presentations: ODP, Drawings: ODG, Databases: ODB, and Formulas: ODF.
2. Some common Microsoft Office file extension are: Word: DOC and DOCX, Excel: XLS and XLSX, PowerPoint: PPT and PPTX, Access: MDB and ACCDB.
3. Other extensions can be found at: http://www.file-extensions.org/extensions/common
4. If the file extension you want is NOT in the list: click the New button then enter the desired file extension and click OK. The file extension will be added to the list. Proceed with Step 5.
Note to Step 15:
5. For Word files select: swriter.exe, for Excel files select: scalc, for PowerPoint files select: simpress.exe, for Access files select: sbase.exe
I use LibreOffice 3.5 on Windows XP.
On my way from A TO Z, I often end up AT OZ.