I can't remember off the top of my head whether the regular lamps are 3 or 5W. I think 5W. You need to put a resistor in parallel to get rid of the fault but its got to be of the correct rating (minimum 50W as you will struggle to get a suitable heatsink there) and will get hot. If you can follow the loom and maybe mount it somewhere on the bodywork of the boot that would be OK.
Assuming the LEDs are around 1W each, you need something to make up the other 16W, so a resistor of 8 or 10 ohms would be about right.
OK, that's all the electrical stuff.
If you've fitted anything other then warm white LEDs then you've probably decreased the overall brightness of the lamp. The red plastic on there is designed to work with incandescent lamps which have a fairly broad light spectrum. LEDs have a very limited spectrum and are often filtered by the coloured plastic to leave not much useful output.
