Hex code from SD card writed to "main" code

Hi I want to do something like "downloading" hex code from sd card, write it next to my main code (for example Main menu or something) and start this "downloaded" code (ex. game). I was reading all those topics on forums but i can't find that what i want to load code from sd and stick to main menu code (beacouse after reset i think there would be same game after loading) and it needs menu to delete (and load from sd main menu static code) game code and let menu be like at the start point.

You can get most of what you want with my standalone programmer. Load up to 256 sketches on SD card, select one to download into your gaming system with the rotary encoder, press Start button, wait a few seconds.
I don't know if the bootload area is large enough to put the same functionality all in one processor with a '328P. Might have to jump up to a '1284P (128K flash/16K SRAM, up to 4 Kbyte bootloader) or 2560 (256K flash/8K SRAM, up to 8 Kbyte bootloader). Maybe add a check of reading the start button on power up to determine if you start the process to read the rotary encoder & select a game for download, or just start the currently loaded game (if one is loaded).