Yep that's the answer RASTABT.
Also bear in mind that there won't just be the one LED, there will be quite a few, maybe even into double figures.
I did the exact same thing to my Nokia 7110e. Changed from the green to blue. There was about 15 LED's in there including the keyboard and screen. I already had the surface mount blue LED's and luckily as I'm an Electronics Engineer, I had the surface mount soldering equipment. You can use a normal soldering iron but it will have to have a small bit and not be a 100 watt monster. You'll have to be very careful and not apply too much heat or you will damage your phone.
I changed the LED's on mine not out of 'cooliness' but I stupidly dropped my phone while I was washing my hands. You know the old holding the phone against your ear with your shoulder? Well I dropped the damn thing, it went into the sink at one side, zipped along the sink and shot out the other side like a skateboarder on a quarter pipe and landed in the toilet. Taking the phone apart and letting it dry out was the only solution and while it was apart I thought I would do a few changes
Even though the phone was switched on at the time it went into the depths of my toilet, it still works just fine. Good thing I had just flushed
although the phone did smell 'pine fresh' for a few days afterwards...LOL.
....DreeM