First of all unpack your data.pak with the unpacker, you can find it here:

. When you have unpacked it go in the new data folder that was created to data\share\creature\monster.csv.
open it and search for the monster you want. When you found it simply copy the line and search for it in Winhex.
For example the monster "Penril Knight"
In winhex you should see this:
1503,Penril Knight,0,27,30,4737,0,149,213,10,50,2,6,0,0,0,0,0, 0,0,5,0,0,1.8,4,1,1,fenrilknight,작성중,353,70,95, 35000,
1,1,2,120,92,104,104,2,18,4,323,404,13,30,2,2000,10 00101,0,0,0,0,0,0,0,0,0,0,13,30,0,0,0,0,0,0,0,0,0, 0,0,0,0,13,30,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,12,546,13,455,13,273,0,0,105,485,106,404,106 ,243,502,5,401,61,202,873,451,142,0,0,0,0,0,0,0,0. .
to change the mopb into no-aggro you have to change just one number its signed red, its always the 5th number after the 2nd name.
1503,Penril Knight,0,27,30,4737,0,149,213,10,50,2,6,0,0,0,0,0, 0,0,5,0,0,1.8,4,1,1,fenrilknight,작성중,353,70,95, 35000,
9,1,2,120,92,104,104,2,18,4,323,404,13,30,2,2000,10 00101,0,0,0,0,0,0,0,0,0,0,13,30,0,0,0,0,0,0,0,0,0, 0,0,0,0,13,30,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,12,546,13,455,13,273,0,0,105,485,106,404,106 ,243,502,5,401,61,202,873,451,142,0,0,0,0,0,0,0,0
This way is just working for non-rangeattack mobs it a little bit different.
Therefor I will show it on the monster "Penril Hunter":
it first should look like this:
1502,Penril Hunter,0,27,31,4994,0,155,222,15,70,1,6,0,0,0,0,0, 0,0,40,0,0,1.8,3.2,1,1,fenrilhunter,작성중,366,74, 101,35000,
3,1,2,104,70,50,50,2,18,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,205,2 94,13,31,
14,3900,3000001,205,0,60,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,13,542, 14,452,14,271,0,0,105,482,106,402,106,241,502,5,40 1,61,203,867,450,141,0,0,0,0,0,0,0,0..
Here you have to change both red signed numbers the 3 into a 6 and the 14, its the Cell-Range, into 00. So in the end it should look like this:
1502,Penril Hunter,0,27,31,4994,0,155,222,15,70,1,6,0,0,0,0,0, 0,0,40,0,0,1.8,3.2,1,1,fenrilhunter,작성중,366,74, 101,35000,
6,1,2,104,70,50,50,2,18,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,205,2 94,13,31,
00,3900,3000001,205,0,60,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,13,542, 14,452,14,271,0,0,105,482,106,402,106,241,502,5,40 1,61,203,867,450,141,0,0,0,0,0,0,0,0..
I hope this can help you a bit to lvl