Is an oath considered binding if the swearer intended to repeat it without actually uttering it again, and what are the implications of this in terms of expiation if the sworn-upon act is performed based on the assumption that the oath was not binding?

If you swear not to do something, and then wish to add something else similar to that oath, intending that the two phrases are akin to a single subject, then you are bound by a single expiation if you break both. The consideration here is the non-multiplicity of the object of the oath and the regard of the two phrases as a single oath. It is important to note that a valid oath is one sworn by the names and attributes of Allah, and one should avoid excessive swearing.