The resin certainly has active material in it, but it also has a lot of nasty shit (PCAs and other combustion products) that normally condense out on the inside of the pipe (to a greater extent than the THC). It is hence more unhealthy than weed, probably by a significant margin. PCAs, the tars produced by incomplete combustion, are carcinogens.
You do not have to cook it to activate it - the cooking is normally needed to decarboxylate it (the vast majority of what we talk about as THC in the plant is THC-COOH, with a carboxylic acid group on the 2-position - that falls off at elevated temperatures). Since you've already smoked the material that is in the resin, you don't need to worry about that.
However, oral bioavailability will be poor (and more importantly, unpredictable) unless it is coadministered with something oily - preferably you would mix the two prior to consuming the resin).
No, plugging will not work very well if at all. Plugging is for water soluble drugs.
All that technical discussion aside, I have trouble imagining being so poor and desperate that i'd smoke fucking resin, let alone eat it. There are more preferable options.... (buy weed, or failing that one of those blends, or failing THAT, buy some pure JWH/CP over the internet and smoke it on foil, or just stay sober). Any of those are probably better options than eating filthy resin, but it should work.
Regarding drinking bong water - i'd expect that very old bongwater, shaken well, could be active, due to particles of THC that condensed near the edges of the bubbles and became suspended in the water. Drinking bongwater though is just fucking retarded.