Not possible without some major client modifications, only other way would be to modify the Windows hosts file.
You are probably trying to do something so people cannot find your IP. This is useless as finding a server IP is so easy anybody can do it no matter how much you try to hide it. Once you are connected to the server your IP is available and can be found.
Ask this person where he got it fom. Perhaps he bought it himself and the pack is locked to his IP. Aside from that changing it in the .ini file should work.
All the values are done in 100, meaning 400 would be 4x, 5000 would be 50x and 350 would be 3.5x and so on.
The last two values are for quest rates, but be careful because unless I am mistaken they also increase the amount of adena certain quests take away.
Moved to correct section.
The error is telling you the problem, it means it cannot finds the correct load class. Check to make certain you have the correct libs directory in your server directory and try again.
This would probably be your best option, but delete all existing HexID's before making a new one because if you do not the system will keep adding new entries to your MySQL gameserver table.
Find an extender that has the option coded into it, or pay an experienced developer to do it for you. If the pack you are using does not have it already there then you won't be able to have auto pickup, this is not l2j. :D