I tried to look up bolt modding, but there was little instruction on how to put an extra hole to put that extra key, and move around stuff for that big L-enter key? All I got essentially was " A bolt mod is simply the replacement of these plastic rivets with nuts and bolts."
Model Ms are designed in such a way that IBM didn't need to make different sets of top barrel plates or membrane sheets depending on what layout they were targeting a given keyboard for...when you're a world-wide conglomerate and you sell a bunch of SKUs into a bunch of international markets, it's nice for inventory management purposes to be able to use the exact same part to make multiple different variations of a keyboard. Thus, you can add/remove/relocate stabilizers and flippers+springs if you tear apart the keyboard. In an ANSI Model M, all of the sensing pads for the ISO keys that aren't present to the user are all there...they're just hidden. So if you remove the stabilizer in that barrel and replace it with a spring+flipper, that newly-revealed key will indeed work.
The reason you are being told to "bolt mod" is because given the way that Model Ms are constructed, there is no way to do this kind of change to a Model M's layout non-destructively. The inner keyboard assembly is not held together by easily-removable screws, but rather by (intended-to-be-)"permanent" plastic rivets. Therefore the only way to gain access to put a flipper in a place where there currently isn't one is to drill off all of the rivets. And after you've done that, it's not really feasible to re-rivet that "sandwich" back together. So you are forced to do a so-called "bolt mod" (or "screw mod") in order to change the layout from ANSI to ISO. It's unavoidable.
