It's not possible with se-tool box 3.
This is the way to do it, at some phones it works and at some it doesn't. We don't know why! DO keep in mind that transparency will not be shown.
QUOTE (Photographer)
1. Get readDB3150.exe by den_po
2. Get ImgToolDB2020
3. Get a MAIN_GENERIC.mbn for your phone (K850_MAIN_GENERIC in your case, search on topse.ru, they have it)
4. Drag the main to the read tool
5. open the .dsk file in the imgtool
6. find the image you want to replace
7. save the image you made yourself as *hexname*.png so for example E4DE.png
8. upload the E4DE.png to tpa/preset/system/icons (If it's not there yet create it)
9. Boot your phone and see if it worked