These are just general tips that could help people to merge mods correctly.
1) .RAW, .BINDAT and .BINLAYOUT files from any mods, can be entirely ignored. These files are automatically generated by the editor, so you don't have to copy them for merging purpose.
2) Use programs like Notepad++ to merge codes between .DAT files easily. Sometimes its much quicker than editing through the editor.
3) Make a habit of restarting the editor every time you've done a good amount of editing/code merging. This to ensure that it detects new changes correctly.
4) If, for some reason your edited/merged file didn't work, try deleting the related .BINDAT/BINLAYOUT files and restart GUTS. At some rare occurrence, you might need to delete the EDITORMOD.MOD of your current mod as well.
5) Sometimes when you unpack a mod (usually happens to a mod that changes or adds a lot of stuff), GUTS will throw a bunch of errors like this : “found property name with a hashcode XX that has no match in tags.dat”. This error is known as broken tags.
If you open the corresponding .DAT file, you'll notice an odd code that consist of long numerical hashes. This is anexample of such error. Did you see something weird about the code? It's in the line “<BOOL>2770992901”
While this error can be left ignored, some of them might be a part of a crucial code that determines the functionality of a certain aspect of the mod. So if we goes by the example, the broken tags in the triggerable might causing the related skill to be buggy.
Ideally, to avoid running into unexpected issue, you should take note all of the broken tags, determine which one of them are affecting any important .DAT files and try to guess what were their original tags. You can use Chton's tool called TL2 Tag Fixer found in here to guess those tags.
A bit of information about outdated mods. There seems to be a misconception about them that are widely spread among players and even some modders as well.
Do note that the mod launcher would display the mod status as “Compiled for outdated game ver”. This is simply an indication that the mod is made for an old version of the game.
Mods would still remain functional regardless of your game version
If the game happens to crash while launching these 'outdated' mods, it is most likely caused by either of these.
Hopefully this puts to end to the misconception.
Trying to add pictures also to this tutorial by Viz.
This short tutorial assumes that you already un-packed the mods you want to merge using GUTS' unpacker utility.
1. All mods have a starting directory inside them named “MEDIA”. What you will do is “merge” these media folders together to create a new merged mod.
As Viz already said, no need to include the .RAW, .BINDAT and .BINLAYOUT files in your merge
2. Just like merging folders containing your data files, you have to be careful about file conflicts. First thing to look for are folders/sub-folders which are duplicated across the mods you want to combine. Of course, for those folders which are not duplicated, you can copy those over into your new-mod MEDIA folder right away.
In the figure below you see the “Unlimited Enchanters” MEDIA folder and the “Epic Encounters” MEDIA folder both have several sub-folders which also need to be merged.
Now you need to check inside and look for more sub-folder OR file duplication. Let's open the DUNGEONS sub-folder first.
3. Good news! The DUNGEONS sub-folder does not have any sub-folders or files which conflict.
So it's completely safe to combine the contents of this sub-folder.
4. Just keep going like this for each and every sub-folder until the source mods are fully merged into your new-mod folder. When you're done, compile your new merge-mod in GUTS and use it in game :D
Obviously the next question is what to do if you there are file conflicts. This is where it gets complicated because you will have to edit those files to try and preserve the changes made to it by the source mods, but still end up with only one file for your merge-pack.
I won't cover such file-editing in this short tutorial because that would really be a LOT of ground to cover! Pls try to read through the other parts of this wiki to learn more about the file that you wat to edit. Then just give it a try! If you get stuck feel free to ask questions in the forums ;)