There you may have a problem.
If you actually tear or cut the tire carcass, the threads that give it it's strength are parted, and the tube inside it is pressurized and trying to push itself out the hole.
So it's like a tear in rough low-threadcount cloth, with you pushing from inside it.
Eventually, more threads will break, the tear or cut will spread, and the tube will spill out.
You can patch that by gluing something to it from teh inside, but since the pressure is also from teh inside, then unless that patch goes a long way away from the tear/cut both circumferentally and up the sidewalls, it's not supported well (pinched) by the tube and the rest of the tire. So pressure from the tube will tend to continue pushing outward, trying to spread the edges.
Plus the edges of teh cut/tear, if on the tread, will wear faster than the rest of teh area around it, cuz tehy will stick out a little bit. As they wear thinner, it may be more likely for somethign else to grab hold of them and tear further, or simply bve easier to poke thru the tire into the tube.
Anything you patch from the outside with (whcih is where you'd really wanna put the patch on a tire to hold the edges together, in addition to the inside to rpevent herniation) will wear thru, and will also be a "bump" on every revolution if it's on the tread area. Stapling or sewing thru the tire carcass to stitch the gap closed also will wear thru.
I've got a number of tires I'd love to keep using but have worn areas or holes in them, and I don't patch and reuse them simply because at that point there's too much of a risk to being stranded from a tire *and* tube failure--and since both will probably go at the same time, if it's on the front and you're braking it could cause a nasty crash.
(If you look in the CrazyBike2 thread, you'll find a post about a General CST tire as I was on my way home from work, that was rubbed thru it's final layer and into the tube as I had to skid to a stop on it. If it hadn't been a super-thick tube it'd've popped the tube and I would nto ahave been ABLE to stop before ending up in the already-happenign collision between two cars in front of me. That woudl've really sucked)
If it is just a small round hole, like nail/etc., it's not such a big deal, if it didn't cut any/many threads.
I suppose you could stuff another whole tire (minus it's bead) inside a tire, and if they're both worn or damaged just turn them so the areas don't overlap. But that's not likely to be very balanced. And it will get heavy....
