All good thoughts.
Perhaps holding a shift / ctrl / alt key while left mousing could easily (?) provide a 2nd default.
My personal default requests:
1) remove tanning tubs from the class of containers, such that when you default boxes / chests / barrels etc to "open", using a tanning tub does not reset them to the (almost never wanted) "Inspect".
2) Keep each user's defaults - not just when disconnect/reconnect, but have a "profile" - a person's favorites, next time you boot up and enter the game.
3) Allow a separate KEY for observe, as you are always switching to raise / lower / flatten etc alternately with Observe. My personal use is to make observe the default, select the others as needed.