I don't know why you would throw a mass cost change as "groundwork". Better see if it's necessary after deiciding on the other stuff, no ?
In general, let's be carefull about changing all stats at once, it makes balancing and testing a lot harder ... It's better to decide the goal of the rework first : in which direction you want this unit to go, and then modify stats to fit this goal.
For instance, answering those questions from last thread would be a good start : Do you still want the mercy to be a snipe tool, but with more consistent counterplay ? Or do you think the unit design is broken and should be something else (last thread mentionned some damage over time on a big area) ? Small tweak to numbers, or big rework ?