hi SoBird and Welcome.
There is a project file
"rk27_baord.mcp" in
C:\rk27sdk_new\Ide\Rk27_board
I open this up in ADS. Then it's quite easy to work in the IDE.
When you sucessfully compile the build, the 4 firmware folders are generated and all you need to do is copy over to the player and reboot.
All the info you need should be in this thread :-
Hooray!!! Rockchip SDK!
However you MUST backup your working firmware first, apart from the obvious risk there is information in it you will need to redo a custom firmware.
Have you tried putting a file called RKLDSET.FLW on your player? That could well open it up. Also AleMaxx has created a linux tool for this purpose too, although I haven't tried it yet.
Also the best place to ask about this is here
Hooray!!! Rockchip SDK! where most of the discussion takes place.
Good Luck!