With the unfortunate outcome of my Skew-by-2 attempt, I felt I might as well give everyone a display of my successes to date.
My very first mod was a Fisher Cube. I did the normal method of cutting (with a Dremel) and filling (with epoxy putty). I glued the cut-off pieces onto the edges, rather than make the extensions from scratch.
My next mod was a 2x2 Square Antiprism. This is a good shape-shifter, but I am considering replacing the repeated sticker colors with different colors. That would make this "cube" a little bit more challenging.
Then, I tried to make a 2x2x1 out of a mini 2x2x2, but the mechanism of the key-chain 2x2x2 was very badly designed, and the 2x2x1 broke before I could sticker it.
My most recent mod was an X-Block. I used plastic sheeting and some epoxy filler. This one turns great, but sometimes the extended top and bottom pieces pop out. I am working on a way to fix this.
Here are some pictures of these three mods, along with my Magnetic 3x3, which I will post about later today.
I'm now working on making a Brilicube by hand, and it is proving to be just as difficult as I thought it would be.