I managed to find out that high temp heat paint can be used on the heat shield and that holes can be patched up using exhaust filler/putty. I managed to add extra tape on the unaffected side to act as a way of preventing the exhaust filler from sagging through. Once set the whole black fibre side of the shield was treated to two thin coats of matt black high temp paint, after which the reflective side was completely taped up neatly with aluminium reflective tape. The shield looks like brand new and I don't have to worry about it setting on fire!