Is it possible to replace the system open file dialog?

Starting in Vista, the FileOpen/FileSave dialogs are now "Common Item Dialogs" of which IFileOpenDialog & IFileSaveDialog are the two published implementations.

Since they're just COM objects with known CLSIDs you might get away with just replacing them by re-registering using their CLSIDs. Never tried something like that, might trip all sorts of alarm bells.

Pre-Vista file dialogs can be hooked in process, but I've never come across anything about global hooks or equivalent.

If you copy a file/folder to a dialog's filename field it usually pastes the full path anyway.

For example, if you have open both a program calling the standard open/save dialog box and also have a window open at the file or path that you want to work with (open from/save to), you can simply copy the file/folder from the explorer window, and then paste into the filename field of the dialog box, and it will insert the full path of the file/folder. No custom script is required!

Alternatively, for those programs that use custom dialog boxes where this step fails, copy the same file/folder in the window into the address bar of the same window (assuming it is visible). This will paste the full path, which you can copy again, and then paste this full path into the custom dialog box. I often use this when creating Office hyperlinks (Ctrl+K), because the Insert Hyperlink dialog does not work for the first method.

You can also use similar methods but paste into address bar fields and it works.