When Can Columns in Table not be Altered and not be Added?

Question

i seem to be getting paranoid over 2 cases listed below. Can someone provide a general list of conditions for:

1. when can columns not be added to an existing table

2. when can columns not be altered

Please skip the reason for same name for either case.

Answer 1

When can these things not happen? When the user trying to do them doesn't have permissions. Users should in general never have these permissions.(incidentally developers should not have prod permissions to do this sort of thing, so that all changes must be deployed with a script that is in source control) In SQL server, you also have DDL triggers that can be set up to prevent changes