B4J Question FileChooser options

I don't think that it is possible. The "overwrite confirmation" message is not configurable.

Then there is any other possibility to achieve this in B4J without building my own File Chooser?

Maybe use DirectoryChooser + another dialog for the file name.

Yes, this is a bit annoying.
This is what I do in my apps when the user wants to save something (through a menu entry or a button): the app creates a unique file name that includes a date and/or time stamp, so that I can be reasonably assured that the file name will be unique, and I place the fully qualified file name in a text box that the user can click to cut and paste into Explorer or other software. I typically place that file in the User's AppData folder "C:\Users\<user>\AppData\Roaming" since that is a place that I know B4J can write to.

It's a little clumsy but apparently my users got used to that pretty quickly.

It is quite frustrating that this folder is hidden by default under Windows, so it is hard to navigate to with Explorer, but the trick above does help.

I need something a little bit different. If an existing file is selected in FileChooser, then that file will be further used. If a new file name entered, the new file will be used. So ... half Open, half Save. For the moment I keep Save, even if when an existing file is selected I get a message that the file will be overwritten, which is not the case (just used).