Thanks to everyone who provided suggestions. In working with Donald Ward, a VW trainer, we developed a detailed procedure that solves my issues and I'm sure others also. I wanted to share it so that everyone may benefit from it.
To convert Landmark 12 plant library to 2009:
Open 12 plant library in 2009 and resource browser. View resources as thumbnails.
When you first set this up, go to the plant tool and double click on a tree symbol and a plant from the standard 2009 symbols (Plant Objects.vwx). By double clicking on the symbols this will add the plant component classes in the Navigation palette to your current document.
Select the VW-12 plant symbol in RB, right click and select edit 2D graphics.
To edit interior linework of symbol:
Select all. Shift and click on outline to deselect the color fill geometry.
With interior linework selected, change class in object info palette to Plants>Component>Interior Linework.
For color fill control:
Duplicate the color fill (Surface object/Circle/Polyline), with the 2D selection tool hold down the option key (mac) or Ctrl key (PC) and move your courser over the color fill. You should see a + sign beside your cursor click on plant outline so that the color fill is duplicated directly on top of the original geometry.
Change the attributes in the attributes palette of the duplicate copy to have a none fill color and solid pen line.
Change the class to Plants>Component>Outline.
Send this class to back with Command + B (mac)or Ctrl + B (PC).
For plant fill color:
Select the (Surface object/Circle/Polyline).
Change the attributes in the attributes palette to the desired color fill or gradient and choose a none pen color.
Change the class to Plants>Component>Color Fill in the object info palette.
Click on Exit Plant box on top right corner.
If you are editing Tree symbols it is best to assign the fill color of trees to the Plants>Component>Canopy class. This will keep consistency with the fill color of tree symbols created in VW-2009.
To control the plant tag, it also needs to be edited.
Select the plant symbol in Resource Browser, right click and select edit definition.
In Default Prefs tab, change Tag Class to Plants>Component>Tags.
This is also a good time to make any other changes to the definition.
Click OK.
This plant symbol now has the same controls with classes as 2009 Plants.
Refer to Tech Tip on the Knowledgebase Adding New Plants to Place Plant Tool to export into plant defaults.
Also note whatever 2D geometry is sent to the back when editing the 2D graphics will be the graphic that shows when choosing Mass Over Lapping in the Rendering options when editing the Definition of the plant (i.e. if the solid color fill geometry is sent to the back you will see the fill color of the plant, if the outline is sent to the back then you would see just the outline of the plant with this option turned on).