You said it involved a lot of work, you gave no time frame for what "a lot of work" is.
You mean other than "a couple times in the last 10 years" sort of timeframe that I talked about? In this case, what I wrote was: "The problem is that you can't put skins into a scenario without them being built into the terrain, and that only happens in the rare case that (1) a terrain is being rebuilt at least a couple of months in advance and (2) someone has done a suitable skin. The odds of it are like the alignment of planets. Getting a skin in for a scenario has happened a couple of times in 10 years. Builds of terrains involve the terrain team putting in a bunch of work, and it has to then be run through checks and cleared by HTC."
That covers it pretty well, but I can rephrase it to explain another way. Normally, it isn't done. When it has been done, it involved (1) a person making a skin, (2) a person rebuilding a terrain to put the skin in (see below for more information on this factor), and (3) Skuzzy recertifying the terrain and releasing it for use on Special-Events servers (a bunch of work for him, but I don't know how many man-hours it is).
Terrains are handled by the Terrain Team. These volunteers build new terrains and rework old terrains that are broken or made non-optimal by updates to AH. They have a large backlog of old terrains to rework or replace, and a queue of new terrains that they want to develop. Take whoever you think is an example of an overworked person (a booked-solid surgeon, maybe, who hasn't spent an evening with his family for the past two months; or a salesman who is in the process of travelling to 20 states and 10 different countries on high-value sales calls) and see if he has a spare day to help you paint your house. It's like that.
And it's not just the work -- it's the timing of it. You have to do the work between the time you pick the plane set for the next scenario and about one month from the start of that scenario. How big is that window? It's somewhere around a few months. So, the skinner gets a month to do his work, and the terrain team gets a couple of months to do the work (or whatever mix adds up to a few months). Those people who do the work have to be available exactly during that specific time period, start the work during that period, and end it during that period. In addition just to the effort involved, the need for it to happen in a particular window is what cuts down the odds of it as well.