[fly_zo]

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