Lazer, I don't think you understand about the two in one key.
On a factory key, let's take Ford for instance because they seem to have had the double cut key for the longest. The various cuts, or indentations, are identical on both sides of the key so you can insert it either way and it will work. Inside the lock are several spring loaded lock pins. When you insert the key, ONLY ONE SIDE, lines up the pins to the shear line and the lock turns.
The cuts on the other side are not used. What I am saying is, cut a different vehicle on the other side, mark the key so you will know which way to insert it, and you have two keys in one. I don't understand your concern that the key blank will be weakened. You just end up with a new key that has different indentations on each side whereas before you did this, they were identical. Does that explain it? It in no way weakens the key blank. There is no difference in the structural integrity of the key after the modification.
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"The more I carry, the less I need."