Can I use IS42SM16160K DRAM instead of IS42S16400 DRAM?
"For some reason " &mdash; don't you know why you want to make this change?

In any case, no &mdash; the chips are in very different packages, and a board designed for one will not work with the other, unless you had the foresight to use a dual footprint.

Furthermore, the chips are very different sizes, so there will be changes required in the configuration of the memory controller as well.