The packager supports all kinds of settings. You can set them with the new #PackagerProperty attribute.
For example to set the icon file, assuming that the ico file is in the Files tab and is named turtle.ico:
B4X:
#PackagerProperty: IconFile = ..\Files\turtle.ico
Also set the executable name:
B4X:
#PackagerProperty: IconFile = ..\Files\turtle.ico
#PackagerProperty: ExeName = Turtle
Note that this will set the executable icon. Set the form icon with the designer. The form icon should be a regular image file (png, jpg, ...).