Gabriel, it sounds like you want to create MIDI files that can use any of the 514 tones of your Casio LK-300TV keyboard. After reading the manual, I think you can create a Format 0 MIDI file with appropriate Bank MSB and Program Change messages to select the tones you want.
Casio LK-300TV manual
The Tone List in the manual, PDF pages 63 to 66 (printed pages A-1 to A-4), lists the Program Change and Bank MSB values used to select any of the keyboard's 514 tones.
If you want to play a MIDI file from an SD card the MIDI file has to be in Format 0 and you have to put it in the MUSICDAT folder on the SD card. Alternatively, you can use the SMF Converter to convert a MIDI file into a CM2 file, then put that on the SD card. In the manual, see PDF pages 54 to 58 (printed pages E-52 to E-56).
If you want to transfer a song to the keyboard's internal Song Bank, then you have to use the SMF Converter to convert a MIDI file and transfer it into the keyboard. For the transfer process, the SMF Converter connects to the keyboard over its USB MIDI port. You connect a USB cable between the keyboard and your computer, then select the appropriate MIDI IN and MIDI OUT ports in the SMF Converter program. In the manual, see PDF page 51 (printed page E-49).