When you 'Pin' something, it won't move right? Mostly.
If a Level is 'Pinned' you will not be able to use the move command or the move by dragging command. You will be able to change the height of the level by edited the Level-Head elevation text. No warning, Revit just moves the Level.
(Let me know if you have noticed this....)
As a workaround, you could draw a dimension to the Level and then lock it.