You can only make design changes when no one else is using it. It is always
a good idea to split a database. You'll avoid corruption problems for one
thing.
In addition, it isn't wise to change the design of reports/forms in a
production database. You would likely want to test it before implementing
it live.
Split the database; leave the backend (tables/relationships) on the server.
Give each user a copy of the frontend (all other objects with links to the
tables in the backend) on their computer. In your copy of the frontend you
can implement and test changes. Once you are finished, you distribute the
updated frontend to the users.
Tony Toews has a utility you can use to automate the distribution of
frontends. See
http://www.granite.ab.ca/access/autofe.htm
He also has links at the bottom of that page for other methods.
