After much research and desk-head-banging our team has come to the conclusion you cannot (due to the dynamic nature of child actor components) modify nested actor blueprint variables through the details view. We are looking for a workaround as our project strongly requires a nested solution.
We are attempting to create buildings out of blueprinted parts, which themselves need to be blueprints. Sections of the buildings are constructed using blueprints with controls for materials, meshes etc (a few are sourced from the unreal marketplace) i.e tileable building blocks. We need to create these in-editor (i.e not dynamically) and want to maintain their blueprint links in case of future modifications of the building parts.
Now the annoying part is (As you may know), in the blueprint editor we completely lose child blueprint variable control if we drag in these blueprint building parts. This means the part blueprints are basically useless as we’re stuck with their default variable values and thus default appearances. Alternatively from the level editor, placing, modifying and then converting our building section blueprints into a single complete building blueprint sort-of works. This has the odd and incredibly annoying effect of converting the selection to the blueprint, and all child blueprints to static meshes, meaning we again lose blueprint control and can no longer modify the existing elements of the blueprint.
So we either have to manually create our buildings with the meshes from the section blueprints and lose all of the functionality we have built into their blueprints (!?), or fight the level editor to blueprint conversion. This entails creating, duplicating and converting every building formation we wish to use, then losing all the blueprint functionality anyway.
Are we missing something?
Interestingly UMG does not suffer from this problem as it provides child variables without issue in a relatively similar structure.
Feature request for this exactly functionality (Not in 4.10): (Feature request) Change child actors variables within blueprints - UE4 AnswerHub
Post with similar issue: https://forums.unrealengine.com/showthread.php?92202-Is-there-some-catch-to-child-actor-components&highlight=Nested
Shocking workaround with structs (!?): Edit nested object variables on Actor? - UE4 AnswerHub
Recent request for functionality: How to access exposed variables of a child actor component via the details panel? - UE4 AnswerHub