Hi David,
From my current environment, (Win7 pro, Uipath 2016.2)
This is not working out for two reasons.
First Sendkey does not inherit selector from Excel Application scope (might be fixed by Moonlight).
Second CTRL+F10 just pin/unpin the Workbook from it’s Excel application container
However the windows shortcut (Win+Up) to maximize windows is valid it would still require to target the selector.
Win+Up can also be pressed regardless if it is already maximized or not.
Just by curiosity, what is the excel version and operating system you are using?
Cheers.