How do I stop Open Office from automatically changing the date format?

This is a special auto-correct behaviour that is only active for tables in Writer (not in Calc). It is controlled under:

Tools > Options > OpenOffice.org Writer > Table > Input in tables > Number recognition

Uncheck that option to disable the autocorrection.

changing the date format is simple just follow these steps: in OpenOffice Writer go to Insert > Fields > Other > select Date from the first box > Date fixed from the second box > Choose the format that u want to use from the third box then Click Insert.

edit: you also can add more formats from the same window if u want by double clicking on Additional Formats.....

For Openoffice Writer:

Change date autocorrect style

1. Go to Table.
2. In Number Format Menu - change Language to English UK or whatever you need - choose date style you want in Format.

Just click right mouse button where you fill date and:

formatcell -> number -> date -> formatcode -> DD MMMM YY -> then click OK button.

Your date related problem should be solved.

You can start with an apostrophe to ensure that it is recognised as a text and hence doesn't autocomplete.