The toolbar buttons on a child panel run in the context of that child object. Since you are no longer in the context of the Change object any quick action you run from here would need the relationship link already established to know which Change you want to operate on or some form of input that tells it which Change you want to link to.
I like the idea but I don't think you can make it happen as it relies on having the data that it is intended to populate.
Does the system know the context of the active tab in this kind of layout?
Could I park these buttons in the Change summary header and only make them visible when the Sites tab is active? Visible if ActiveTab = "Sites"
Thanks for your input!
Unfortunately no, the system doesn't know which child panel you are on is such a way you could make the button's visibility rules based on that.
You could certainly still have a button on the Change form or toolbar to (un)link certain sets of sites but they would still be visible if the user is looking at any other tab like the Details tab as well.
I ended up with a solution we like even better!
The button menu/submenu moved up into the main button bar for Change. This way we don't have to jump into that sub-panel to populate the Sites. Less clicks = happier IT staff.
This button menu is hidden for all Status except Logged, the only time you can make edits to a Change anyway.