This works because the modified site (a CG) will base pair with a GC on its opposite strand. But since that opposite strand runs in the other orientation, it will also look like a CG to the ...

In both scenarios, an additional round of DNA synthesis or repair can yield either transitions or transversions at CG base pairs (including CG-to-TA, CG-to-GC and CG-to-AT base-pair mutations).