open~start up a game file, and in the GUI (editor) mode, on the left pane with the objects' tree, at the bottom (so lower left corner of the editor~GUI screen), is "FILTER", click on this and select the "show library elements", this reveals all of the core~default stuff in the above left pane objects' tree (they're lightly greyed fonted).
Also, I'm pretty sure that if you do make a custom verb or command, that has the same name as one of the built in verbs, commands, and~or etc, then it'll notify you, and prevent you from making it with an error.
if you want to change those default things, then (after you revealed them via the filter -> show library elements), you just click on whatever you want to change (you can also change the stuff in~under the "advanced" too, but becareful as these are more of your fundamental stuff so it has much wider range of what it effects), and then you just on the right side, there now should be an option to "copy" so that you don't change the actual core~default stuff, but are able to change a copied version for use in your game file (or as in, if you're making, a library game file, so that you can add it too another game of yours).
and yes, it would be nice if someone would put these onto the wiki, if anyone would be so kind, to take the time, to do so, lol.
Alex made quest so that you can't mess up the actual quest files. You can only mess up your own specific game files, hehe.