Edit Attributes...
if you get the following message "This operation accesses a dimension containing a large number of elements. The uploading of these elements from the server may take a few minutes. Continue?"
Editing directly the attributes cube is much faster:

• View -> Display Control Objects
• Open the cube }ElementAttributes_dimension
• Modify the required fields like in any cube

Add new Attribute
for large dimensions, it is faster to just create a temporary TI process with the following code in the Prolog
ATTRINSERT('Model',, 'InteriorColor', 'S');
This example creates the InteriorColor string attribute for the Model dimension.

Checking if an attribute/alias already exists
let's say we want to create an alias Code for the dimension Customer.
In Advanced->Prolog Tab:
If(DIMIX('}Element_Attributes_Customer','Code') = 0);
AttrInsert('Customer','','Code','A');
Endif;

So you do not have to worry about the AttrInsert generating an error if you ever have to run the process again.

After updating aliases in TM1, you will need to clear the Excel cache to see the changes by running the macro m_clear or  restart excel.