Ethics of "recycling" assignments

I can't think of a better title, feel free to edit.

I'm retaking a course at university, and the basic assessments are very similar; if I can assume that I'm studying effectively, could there be any issues with modifying my assignments to fit the new criteria, and effectively resubmitting them?

From my perspective, this cannot be collaboration or collusion, but it could be defined as plagiarism, at least by a computer. It makes very little sense to reference my own work (is that necessary in academia?), is it therefore sensible to assume that there will be no complication from an ethical perspective?