Transformer question

Yes and no. The yes part is that you would get a 2 to 1 step up if you connect the transformer 'backwards' on 240v, the no part is that many commercial transformers are designed for one duty, step up or step down. In either case, the intended secondary (output) is low impedance to reduce losses and increase efficiency. This is a problem when wiring it in reverse as the low impedance will cause a large inrush current when powering up the transformer or transient loads spike the current (e.g. starting a motor.) Also the core may be designed to have best magnetic properties when the transformer is used in its intended direction. Furthermore the insulation of the 240v and 120v windings may have a shorter life because of 100% overvoltage in each case. Remember transients & spikes will be doubled in peak value too, which can weaken insulation. These things may not matter so much on a small domestic type transformer rated at a few VA but real world 480v loads tend to be bigger devices, motors, etc. Regulation and efficiency would not be ideal and overheating might be a problem, especially near max rated load. In general, probably not a good idea.