So there is a way u can modify the original to theme to make ur own new theme.
the only easiest method is to edit the xml document of the original theme for new one.
1. Transfer the theme file (*.thm file) from ur mobile to computer through cable or bluetooth.
2. change its extension from .thm to .zip
3. extract the files inside this zip and save in a different folder.
4. also make a backup folder and put a copy there too.
5. now open the xml document.
6. i would recommend to change nothing in this xml coding except to look for the names of images used for background wallpaper and icons,close it without changing.
7. now replace ur files i.e wallpaper and icons if u wish to change, with the original ones u have just extracted. DONT REPLACE THIS XML DOCUMENT,LEAVE IT AS IT IS.
8. note that ur file names and their length and width should be same as that were going to be replaced. Also their format should also match whether it is jpg or bitmap, otherwise your theme will not work.
9. now select all files alongwith xml document and put them in archive with winrar.
10. type archive name, select zip format option and then write .thm with ur theme name
i.e newtheme.thm as shown below
11. now press ok to zip,it will appear as a .thm file
12. Upload to ur mobile and simply install
13. go to the themes section in ur phone and apply it,and enjoy.
Link for samsung themes: