GL Account Structure

We are wanting to change our GL account structure, making the second segment 4 characters instead of 2.  I am assuming everyone needs to be out the system when this is performed because we get the warning, "This task is in use...".  Before we wait until after hours and try, in the list of users locking the file, there are some that do not work here anymore and have no orders open under their usercode.  We will see what happens once we get everyone out, but just trying to be proactive if we can not update the structure and get this same error.