What was the restricting factor on starting in cold wx, if I may ask?
The engines wouldn't light off. They'd taken a 747-8 to Alaska to do some cold weather ECS testing - we'd offered propulsion support but they said it wasn't needed, no engine testing was planned. Well, when they got ready to come home and the aircraft had cold soaked at -30F, they couldn't start the engines. They'd try six or seven times - by which time lots of fuel had puddled in the engine - and when they finally got a light there was a loud bang and great balls of fire out the tailpipe. I think they had to haul the aircraft into a hangar and let it warm up a bit before they were able to get the engines started to come home.
GE played around with the fuel nozzle staging during starts to fix it (the GEnx has a really complex fuel injection system - basically acts like a dual annular combustor for emissions - but without the drawbacks of an actual dual annular combustor - so there are a lot of variables they can play with).
When we did the testing, GE would load a software 'trim' into one engine, and we'd try a start. The first one was OK - definitely an improvement - but the trim the tried on the second engine worked great. We tried that trim on engines 3 and 4 and again it worked great. The trims were not considered 'flight worthy' so they ran all four engines for ~20 minutes to get them nice and warm so they'd be able to get them started a few hour later when it was time to head back to Seattle, then shutdown and restored the original s/w on all engines.
This was going on spring of 2011, and we got type cert and started initial deliveries about six months later. If we hadn't gotten the fix identified in Iqaluit, I suppose they would have needed to head to someplace way, way south to do the test or we wouldn't have gotten type cert when we did.