In SSMS it will not drop a table unless you have the "Allow DROP" option ticked with in the preferences. Also, the only time it will drop a table and recreate is if there is a need to.
Adding a new column to the end of the database table does not but if you drag it around to place it in a specific column order this will. Also, other options you specify as part of the column may cause a drop.
The best way to see this is by either keeping the Allow Drop option disabled or generating a script of the changes before applying them. If the script creates a temporary table then inserts data from the existing table, it is going to be dropping and recreating.