The configuration file for the mod is located in .minecraft/config/HardcoreEnderExpansion.cfg (servers have the config folder in the same directory as the executable).
Configuration consists of 3 parts - block, item and general. In the block and item areas, you can modify the IDs (only in Minecraft 1.6.4 or older) to not conflict with other mods, but the main topic of this article is the general configuration. In the table, there is a list of all settings, values and meaning. If you cannot see a certain option in your configuration file, you have an outdated version of the mod.
Client and server settings Edit
|achievementStartId||number||3500||Starting ID to use for Achievements. Change this around, if you experience achievement incompatibility between mods.|
|enableTempleCaller||true/false||true||Enables or disables Temple Caller's End wiping mechanic.|
|enableEndermanpocalypse||true/false||true||Enables or disables Endermanpocalypse. If disabled, the Ender Demon will spawn in the End instead.|
|gooBattlesWater||true/false||true||Enables or disables Ender Goo reaction to water, which might cause slight lag on slow computers.|
|overpoweredMobs||true/false||false||Increases mob stats - mostly health, strength and speed. Also modifies attack mechanics of some mobs, to make them stronger.|
List of items (and blocks) to disable decomposing mechanic for. Blacklisted items cannot be decomposed, and they will also not be returned as an ingredient for decomposed item. Only in MC 1.7.2 or newer. The list is separated by commas, each entry is case-sensitive block/item name and optional damage values. There are also some special cases, listed in the examples.
Client-only settings Edit
|enableMusic||true/false||true||Controls whether to load custom music. If disabled, music discs will not play!|
|enableUpdateNotifications||true/false||true||Loads data about updates upon loading a world (without any lag), and notifies the user about new versions.|