Does Infopath support a On Save event (well i should say just before save event) and it clears a specific field?
Or is there another way of temporarily holding a value in a field while the form is open and clearing it when its about to save (so that it saves with a blank field)?
If your field were in a secondary data source (like an XML file), you wouldn't need to clear it, since secondary data isn't saved with the form. You'd have to know what to set it to when the XML was re-opened or the form was first opened, of course...
Of course, Hilary's right.
InfoPath *does* support OnSave command but doing any kind of event handling means you gotta write code.
For a simple approach, consider qRules which supports OnSave without the need for code.
Could you elaborate on qRules with OnSave? (wasn't able to google it) - and the data isn't external its internal, but designed to be only temporary for that specific form session only.