"Wogification" loads all WoG (Data/s) ERM scripts into a map. See the ERM Help document for more details (and see the Era manual for how wogification works under Era).
ERM scripts can make changes to a map as the map is being loaded or at the start of day one (or on any day, for that matter). The WoG 3.58f script named script00.erm adds WoG objects and creatures to a map by replacing existing objects of the same size.
The "Dragon Peaks" Era Mod (discussed on page 5 of this forum, the last time I looked) contains a script which allows a player to remove extra objects from a map on day one (to make room to add some large objects):
This is another example of things that can be done to alter a map at the start of a game.
ERM is a (simple) computer language. It cannot be learned in a few hours or days, but by reading ERM Help and practicing the tutorials it can be learned in a few weeks. Once it is learned you can do almost anything you want to a WoG map.
The Era Mod "WoG Revised" contains many new options for improving random maps. See the "Era II mods" thread (on page 1 of this forum currently) for more details on it.