I have changed the block IDs on the config file for the worldgen blocks (always below 256) but I keep on getting the same IDs as the default ones in game, and yea i saved before starting minecraft, i closed the config file too, tried 10/12 times before posting this

Can not reproduce, however the issue likely is that your editing the old config file in config/biomesoplenty.cfg rather than using the ones in config/biomesoplenty/