interim

I would like say that among some position I have held one of them was "interim". For example:

Reception officer and interim Office Manager

OR

Reception officer and Office Manager as interim (though it should mean that both position have been held interim)

OR

Reception officer and as interim Office Manager

OR

I do not have any idea else!!!

???

You could use "Office Manager pro tem," but interim seems a reasonable choice.

Temporary would do as well.