QIs it possible or likely for blood alcohol levels to increase or decrease in a decomposing body, and if so, during what stages of decomposition?
SL
AAlcohol is usually destroyed in the decay process, but it might indeed be produced by the bacteria that cause decay. This means that alcohol can only appear during active decay.
The onset and rate of decay depends on the ambient temperature more than anything else. The reason is that these bacteria thrive in warm, moist environments and become sluggish in colder and drier climes. Freezing will stop their activities completely.
Whether a particular corpse produces alcohol or not is unpredictable. If it does, the timing of this production depends on the conditions the corpse is exposed to. In an enclosed garage in Houston in August, this process will be very rapid, and the corpse will be severely decayed after forty-eight hours. If in a snowbank in Minnesota in February, it might not begin the decay process until April or May when the spring thaw occurs. And anything in between. The appearance of any alcohol would coincide with the time frame of the bacterial activity.