Hi, yes SNEJ have a own Place for Modding you find it under D2SE > General Modding.
For all your changes you dont need to edit the code. There are 2 way. One is to edit the code which is only with 101010010 and so on, so u need a hex editor and a program that u can read the binary code as assamber, but its much harder than the other way. The easier way is to edit the .txt files. You just need a mpq editor and a programm like excel. But not every thing is change able with .txt edtitng. But all your changes you can do with it.
http://phrozenkeep.hugelaser.com/index.php?ind=reviews&op=section_view&idev=4On this site are the .txt explained. How you can export and import the .txt files from .mpq files you better read a guide, there is probably a guide on this site, too.
Max lvl > experience.txt
stat per lvl > charstats.txt
skill points per lvl > there is no column for it, but u can do it with .txtediting too. there is a guide for it
edit items > here are many .txt it depends what u want u edit
some examples:
base items > armors/weapons/misc.txt
sets > setitems/sets.txt
uniques > uniquesitems.txt
and you can change a lot more like preffixes and suffixes of magic or rare items and make other automod and so on just look at the names of .txt
monster gained exp > monstats/monlvl.txt