"Anyone recommend the best tools to use before i just delve in and balls it all up?"
Yep - get yourself a Dremel - or a good quality Dremel knock-off. Using a cutting/grinder disk - you'll be able to cut through that like melted butter. Cut at least 1mm (maybe a bit more) away from the true edges (if that makes sense), then use a high grit sandpaper to smooth the edges down until you're satisfied with the result, etc.
Make sure you use a mask - fibreglass is nasty stuff to get in your lungs. The Dremel will produce a lot of fine dust.
I've been using a knock-off Dremel for years. Was in a hardware store yesterday - and they were selling a genuine entry-level Dremel for about $49.00 Australian Dollars, which is great value. You can also get one with a flexible shaft/handle, which makes fiddly work easier than using the normal Dremel tool.