If you get huge list of errors about case sensitivity, you must fix the game installation path to be case sensitive from file -> preferences -> game installation path. Next time when you load any terrain there wont be game installation path case sensitive errors.
Giants Editor (GE) got v8.1 release on 2019-02-09, new features were toggle options for interactive placement mode. S Scale new objects randomly (range according to preferences), C Don't place new objects on objects created during the current session, T Only place new objects on terrain.
Use file -> preferences -> viewport -> interactive placement scale variance. This will set the object placing using CTRL-B with random scale.
HOWTO use new interactive placement for trees. Select a tree, press CTRL-B, click and HOLD LMB somewhere on the terrain. Now in bottom of GE status bar you see new options "Interactive placement: align to normal 'B' (Off) random scale 'S' (Off) self avoidance 'C' (Off) terrain height 'T' (Off)". While LMB down you hit B, S, C or T keys will turn on/off these toggles. Press left CTRL to place (duplicate) object into the location it is at. Once you release LMB the selected object is placed and interactive mode turns off.
Converting old terrain. Use file -> open mod, then browse to your terrains modDesc.xml file, rest is just clicking OK button and seeing what happens. While its processing be patient and wait, GE looks like its doing nothing but it is processing something on the background, you will get notification when its done.
When you change _density image resolution you must run GE -> scripts -> fs19 -> map -> create ground collision map.