[mistersquid]

> You can do exactly this with BetterTouchTool.

Zooom2 allows for moving/resizing of background windows. Last I checked, BetterTouchTool window manipulation required clicking the window which brings it to the front.

[dbalatero]

This free Hammerspoon plugin will also resize background windows: https://github.com/dbalatero/SkyRocket.spoon/

[evan_]

It's actually configurable in BTT whether you bring the window to the front. You don't need to click, just hold down modifier keys.