[MB-BOB]

you could as well do it with the tools already available. use one of the test runways that you can place in FMB. an invisible one, marked with crosses or tapes for example can be placed basically anywhere on the map where you have leveled ground. also it is possible to land the 163 on any level grass field.
make sure you aproach around 210km/h and a very flat angle. I find it pretty easy actually to land in the grass area next to the concrete strips.

but other than that, you you indeed have to mod the Map.

as i understood , he wants to replace existing runway (concrete) with grass one ..... so map must get modded

regards
Z

If there were a way to adapt the current airfield without modding the map, that would be fine, as I want to create as little work for someone here as possible. If Vampire_pilot's suggestion would accomplish this without modding the map wholesale, that would be great.

All I really want is the current airfield with the taxiways to either side overlaid with "one of the test runways that you can place in FMB. an invisible one, marked with crosses or tapes ." That would work. If that can be accomplished in FMB, that would be simple, as it would (I think?) not need modification of the default map, but would rather be a parameter of the MISSION, itself. Do I understand this correctly?

I can send someone the mission file for fiddling. As noted earlier, I have tweaked the Me163 fuel levels to the proper 7 1/2 minutes of flight duration, and have built an accurate 24+ plane formation of late war B17s to fly against. Whole mission (take off to landing) lasts about 12-14 minutes. Lots of compact timeframe fun.