allow documents to be added to superior item even if the item is completed

when you right click an email with a document, and save to eway crm when we try to select a superior item, you cannot select a completed project. is it possible to add a toggle so we can show completed projects within the superior item box? The reason being is, we can still have documentation for a completed project after its completed, but it still needs to be marked as completed and we don’t want to leave it open up to 6 months after completion, I understand that not every one would want this hence the toggle possibilities in the settings to disabled/enable?