How did you "load" your friend's RGW map into KingGen? Did you place the map's seed into KingGen, and then hit "Generate world"? or did you just hit "Load world" and then browse to, and select the map's folder? I think KingGen's "Load world" is looking for a KingGen - generated map to load - not an RGW map. It
will however, load and create a new map from
any seed it's given - and from anywhere - any name - any number..
As far as creating an island in the middle of a lake - I reckon BFT2020's method is probably correct and the easiest choice: that being said - almost every part of map-making can be regarded as a "hassle" if you like, but I think most folks (here) regard it as a fun "learning curve". This is the very practical application of real-world graphics technology, and we all had to start learning about it at sometime or other, if we want to make 7D2D maps.
That "tree problem" was very significant for me, at least. I'm retired, not particularly "graphics-savvy", and I'm sure I've spent time on at least fifty maps - over perhaps ten weeks - learning to use KingGen. and I'm still in the dark about many parts. But I needed help, and found it here. I didn't expect it to be as complicated as it turned out - but that's the way life goes sometimes.
Just find some patience: do a load of experiments: check out dm and cm; find the seed from the RWG map and use that to remake your friend's map in KG. The seeds work, and will give you ability to
really edit a heightmap - the way you want. And any other component that makes up a complete world.
Remember - it's just a hobby.
Good luck.
pj
PS: Did I mention Tallman Brad's videos from the beginning of this topic, and his own YT channel?
https://www.youtube.com/channel/UCiB9O0IlKrndytqNZ0pFdug
or Capt Krunch's forum page here: