This will only work if you truncate the table or delete all its rows before switching the new table into it, since ALTER TABLE new_table TO old_tableonly works if old_table is empty. So it isn't a single command instead of two, it is still two commands.

Another way (slightly more complicated, because you eventually need a drop statement anyway to tidy up) is to use two rename statements instead of a drop and a rename - this means you can keep the old contents until you are sure you won't need them, and rename back again if you do need them.