Shadow Weave is not supported on the server as far as I know. However, for some casters its use would be ICly interesting and appropriate to pursue, even if there weren't necessarily any game-mechanical changes. So my question is, under what circumstances would it be appropriate to roleplay the use of Shadow Weave? Would you have to work for it in game and would it require an application, given that Shadow Weave can only be used with Shar's sanction?

It would require an OOC application, particularly as shadow weave is one of those secrets that no PC in EfU knows about it.