are you talking about the attachment field type? if so, no I don't think so, but not 100% on that. You can always use the hyperlink address of files though, and use the followhyperlink method in VBA to open the file.
When you double click on the attachment control and choose Add from the box that pops up in my case my default file location is shown as Libraries > Documents with a list of files in that folder.
I don't want this to be the default path I want something else.
I don't use the attachment field and can't answer for sure but, every field has a default value property in the data tab of the properties window. Have you tried that?