I got 8000k Hella HID kit for my old car.
Since i got my new 8, so took out the HID from the old car.
My 8 has it's own HID which is 6000k, but i want to use my old one (my old one is H4 Light Bulb).
I open out and check out, 8 is using the plug in one, but my old one is using the cords directly connected to the power supply.

Is that possible i can change it???
and is that any way i can change the light bulb??

 

If you want to use those old ones in you RX-8 (?) you will need new ballasts, the H4s have seperate ignitors.

S

 

If oyu want 8000k lights on your 8 the easiest way would be to buy 2 bulbs for 100 bucks

 

You need to reword your question to help us better understand. Did your rx8 come with HID's stock or is it an aftermarket kit?

Also, might I suggest a search.

I see a few threads right at the top.
https://www.rx8club.com/search.php?searchid=1104621