my hope for being able to just tweak and not have to replace in MSFS is because unlike previous stock airports these are *so close* to being fine as-is. I've just finished surveying all the airports in NJ/NY/PA/DE/MD and the general result is that they are all perfect blend-in recreations that just need their socks/beacons/slope lighting properly positioned and maybe some buildings adjusted. It's actually ironic how good they are that it becomes even more frustrating to notice the little things that are not correct and not be able to fix them in a few minutes and enjoy
You can check out my KASH airport release on
www.flightsim.to where I did just that, replaced a bunch of the hangars with default hangars and added some more detail to the airport. I did not have to create an Airport object to do that, I just suppressed the buildings with Polygons and the massive beacon with an exclusion rectangle. I don't know if the exclusion rectangle works for windsocks, but it might, it did for the beacon.
In order to suppress fuel stations, however, you need to suppress the whole taxi network, so that requires an airport object and exclusions of items as Jon suggested. To redo the slope (I assume you mean ILS slope?), you'll need to create an airport object for that. So as rev 2, I ended up redoing the whole airport. I wanted to correct the parking anyway, and the runway and lighting needed fixing. I still kept a bunch of features though (like the hangars I had kept (which wasn't many), just replaced the runway, taxi network and aprons, it already doesn't have procedures (not many GA airports do for some reason), so I'll be adding those, too. And other features. I'm nearly done.
Their is only one beacon object in the library, and it's pretty big. I reused it and scaled it, but the beacon light doesn't scale in position with it... sigh. So I put two beacons there. One at the size I wanted without a beacon light, and then put another in the same position, but made it super small so you can't see it, and then positioned its height for the light to be in the correct position. There are probably better workarounds.
The issue that I have with adding a beacon in is, they are on 24 hours a day, they don't follow the day/night/IFR rules that FSX beacons do, and I don't know how to fix that.
The thing that's really bugging me, though, is that in adding more parking, I've exponentially increased the amount of ambient traffic, including vehicles that would never be at my airport. I found a thread describing how that Living World system works, but so far I haven't figured out how to get it to work to my liking.
Also the light row object isn't working properly (known bug), It seems to basically put in the first and last light that you specify, even though it looks correct in Dev Mode. Given how bad the default taxi lighting was, it looks good enough to me. The workaround is to create a single light row object for every light. I'm not doing that, not to mention the other associated bug is that it doesn't create a light in Dev mode for the first point you place, but does for all the rest of the points you place, but that's the light that works in sim mode

... I'll wait for them to fix those bugs and live with the taxi lighting as it is. There's not a ton at my aiport anyway.
For the runway, I had to create the threshold arrows in the xml by hand. It stuck.
32 doesn't have approach lighting, but it does have REIL and Endlights, but everytime I add a Primary Approachlights=None Endlights=True REIL=True card to the file, it deletes it when I save the scenery (even if I add it before I open the project), and it ignores those checkboxes in the Runway options. It'll keep it if I add the card after I save but before I build the project. I wonder if I make 14 the Primary, maybe the lighting options will work more properly.
All these issues could be bugs or things I'm doing wrong. Just passing along my experience.