Start by being in a style like the one you want, except for the feature you want to change. Click on the button for a New style, and it will be "based on" your old style by default. This is essentially making a copy of the existing style. Set the paragraph formatting to right justification and give it a name that will help you remember what it does. By having the style based on your other style, if you change something other than justification in the original style (i.e., the Font), it will change in the new style, as well.

• Understanding Styles in Microsoft Word
• Managing Word Styles by Suzanne Barnhill, MVP