It's worth a try, maybe you can solder them together, but my guess is that the new 12 footer is going to have a different sound than the 8 footer, but you never know!!
connecting two speaker cables together
I have two speaker cables, both the same make and model. One is eight feet long and the other is four feet long. Both are terminated with spades all around. Is there any way to connect the two together, without removing the spades, so that I have one twelve foot cable?