So I have noticed this and I am not sure how relevant it is (probably not) but…
I have seen how in Age of Mythology players do this thing of queueing techs before the building is built by selecting a group of multiple buildings and clicking on the tech that shows up.
While this sadly doesnt work for aoe 3, I have discovered a similar thing but with hotkeys
So for example with rice paddies (and fields) there is a toggle that switches between gathering food of gold. the default is food and you have to click on the toggle to switch.
However, if you select the foundation for the building (before its built) and hit the hotkey for the toggle, it will still switch the toggle for the building, and once its built it will have already switch the which resource its gathering
This also works for Factories and say the Porcelain tower, the default is gold but if you hit the hotkey for say gathering wood while selecting the foundation before its built then its built it would already be switched to wood
This also works for dojos, golden pavilion, shrines and even the ceremonial plaza (ie you can switch the ceremony before the thing is built)
But…sadly it doesnt work for the summer palace because there are no hotkeys for toggling between the armies (summer palace hotkeys pls)
will this be of any use? not really it barely saves you time- like half a second between switching but its neat