Black blob chips are really called COB chips (Chip On Board), its basically like an ordinary IC, except it is made on the actual circuit board and covered with a "blob" of black epoxy. This is a cheap way of mass producing a circuit board with a specific (but limited) set of functions.
There will usually be coppertraces on the circuit board going to the black blob, these can be treated like the pins on any ordinary IC.
Theres no "general bending rules" for black blob chips, as allways there's trial and error.
Many black blob chip toys does not have too much bending potential, because the functionality you would typically spread over 2 or more IC's in a traditional design is now all under the black blob where it is inaccessible to bending.
This doesen't mean that they are useless for bending, try to take a look at my site http://www.mikmo.dk
most of my instruments are actually of the black blob type. There's also examples of what you can do to expand the possibilities of balck blob toys by adding a little circuitry of your own.
Frequently there is a pitch resistor close to the blob. This is especially true if the toy is of the type that plays back samples. This resistor controls the playback rate and can be replaced with a potentiometer to give you pitch up / down control. sometimes it's not close to the blob. Sometimes it's not there at all.
Hope this helps a bit.