How do I get ER Studio Data Architect to automatically add SCD Fields to my Dimensions? This is my first try using this tool and Google searches have been fruitless. 

How can I get ER Studio Data Architect to automatically add the SCD Maintenance Attributes (fields) to the tables I specify as Dimensions? I'm talking about StartDate, EndDate, and RowIsCurrent? 

I'd love it if I could specify those fields and their data types once and not have to mess with it again and again.
If you have already created these entities/tables, there is a sample macro that comes with ER/Studio that does just this.  You'll want to run this on a test model first as you may want to customize it to get the exact results you want.

The sample macro is named ADD BASE ATTRIBUTES TO PERSON ENTITY. You, of course, will want it to work on all or selected entities.   You could customize the macro to add these attributes based on the table being selected.

If you want this to happen for new entities, you can create an entity/table that contains these common attributes/columns, then use that as a template.

I have created a macro to create tables with all the properties I want to be common.  The advantage to doing this is that macros can be tied to a hotkeys, making the creation of the new table easy.

If you don't have the resources to mess with a macro, you could do the workaround of creating a new set of Domains (reusable attributes) in their own folder.  Then you can at least quickly grab all 4 or so and drag them on to the tables.  Still manual, but only once per table.

So the answer you are looking for is dependent upon what the status of your model is currently.