A problem I have.

I'm a modder, and am making a mod for medieval 2 total war, and I found that there is a giant grey area around modding - and this line from the EULA concerned me most :
(f) reverse engineer, derive source code, modify, decompile, disassemble, or create derivative works of the Game Software, in whole or in part unless provided for in section (j) below; ( this is from the EULA as supplied by CA and/or SEGA)
and their is a large grey area surrounding mods and I am worried as from this I can assume that modding is illegal, and I was wondering if anyone knows the legalities of a mod using book information ( but not necessarily names or images ) is breaking multiple laws?
i think this is a important grey area that i want more information on.

Well it is a grey area. But usally companies don't do anything about it when you don't try to use this stuff commercially.

I think the way things work is: if we don't make money from the mods we can make whatever we want. We have LOTR and Warhammer mods for RTW, as well as plenty of major mods.

And what does section j) say?

section J states that you cannot use the supplied editors to creat anything obscene or in violation of intellectual property rights :
use the part of the Game Software which allows you to construct new variations ("Editor") to create new levels which (i) can be used otherwise in connection with the Game Software; (ii) to modify any executable file; (iii) to produce any libelous, defamatory or other illegal material or material that is scandalous or invades the rights of privacy or publicity of a third party; (iv) to use the trademarks, copyright or intellectual property rights of any third party; (v) are then commercially exploited by you (through pay-per-play or timesharing services or otherwise). For the avoidance of doubt you are solely liable and responsible for any claims by a third party resulting from your use of the Editor.

You agree to read and abide by the Game Disc Precautions and Maintenance Instructions and the Safety Information which is set out in the documentation accompanying the Game Software.