You won't be able to change the default name of a workout on our site (those are auto-generated), but you will be able to associate a given workout with a special name for your members. For example, if, for whatever reason, you don't call Fran "fran", but instead it is known to your members as "Jane", you can display it that way for them.
After finding/building your workout of choice and selecting is as either a "pre", "main", or "post" workout for a given day, type in a custom name in the "Title" box on the overlay that appears.

The workout will appear on the Plan calendar and each members' Whiteboard calendars in this format: "custom title workout name"