Yes they are easy to replace as a whole but expensive since when dealing with composites (unlike metals) entire wings and fuselages are one piece items... so if you were going to replace the wing tip on a harrier (for example) and not do a cast repair then you would have to remove and replace an entire wing not just the affected area.... in the 787's case this would be even more extreme since the fuselage is built in large high volume legnth and area pieces so to do what you are talking about might mean removing and replacing an entire third of the fuselage at a time... the better answer is to patch, sand and blend with more composite... much cheaper.... as for using composite in high pressure areas.... well answering this question is much more compicated since there are several factors that go into this......but to make a very long answer short... the first issue is which material truely is stronger or more flexable and more suited to the job??? then if we do decide to put composite and another material together how do we attach them??? a piece of composite may or may not blend and adhere to other materials... if they will not adhere or blend to each other should be use some sort of bracing or plating to attach them???? and how strong is the bracing or plating also by the time we do this is it really that much stronger and whats the cost??? if there is any additional cost is the extra stregnth or benefit worth it??? and the list continues... if the composites turn out to be worth it then they will be used if not then stick to conventional materials.... Hope this helps answer the question... Back to my wine now.... It''s Yellow Tail Chardonnay tonight............