1) What do you call poking around in the memory addresses of a Rom?  Is that considered Romhacking?  I know, I know, I'm one of the great unwashed compared to game modders, but I honestly don't know what keywords to use to look for fellow, uh, hands-on cheaters.

2) Regarding the above: What's up with multiple duplicate address ranges?  Where, say, B12x, C12x, D12x, E12x, etc all show exactly the same values, to control the current music or graphics or whatnot?  Why not just use one set?  I have done non-rom programming, so I can generally tell what the data is doing, but goodness, I don't get this at all. 

Thanks.

I'm pretty sure what he's talking about with #2 is called "mirroring".

Like when different memory addresses point to the same place in the ROM, right?

According to http://en.wikibooks.org/wiki/NES_Programming the mirroring appears to be a function of the NES itself.  That explains why I run across it so often! 

Still slightly boggled as to how this could be helpful.  ...Page swapping, maybe?

Yeah, that's mirroring. Various sections of some of the NES games I recently translated were mirrored; it made finding data (and free ram space) an interesting but enlightening task.

When we tinker with ram, it's usually targetted tinkering. For instance, I figure out which parts of ram are "empty" or overwritable, and which parts are related to the routine I'm working with - a decompression buffer, tilemap prepped for vram transfer, equivalency tables, that sort of thing.

Otherwise, if I fix values for cheat purposes, it's usually to try to get to a particular part of a game as quickly as possible. It's pretty easy to do; most emulators these days have a cheat searcher module that'll do most of the work for you.