Jesse,
unfortunately theme editor can not change graphics in the way you described; you should send a feature request directly to Cakewalk instead!
...
Duckbar Newsletter - Day 5 
Screen capture 1: Import entire folders containing resource files from disk

Screen capture 2: Export selected theme resources to disk (as PNG, BMP or COL files)
Good news!
Import / Export
Batch import/export works now. You can
- Export selected (or all) original or themed resources to disk
- Import resources from png, bmp and col files; either by selecting file(s) or entire directory tree.
Clipboard
- Windows Clipboard copy / paste support added.
File | save
- Save as .sth theme works.
Todo: save preview image, too.
File | Open
- Theme Editor can read current theme format perfectly.
Delete from theme
- Works.
Copy original -> theme
- Possible from context menu and from the main menu
Edit
- Edit single resource image in external editor works.
- To do: Edit color - redirect to Select color.
Resource Preview
- Preview pane size follows main window size. Preview images are cropped to fit in window.
- Original and themed images have their own context menus.
To do: improve.