First of all, I must say this mod is really good in adding game content. Practically just by adding extra skill tree gives a hell lot of new gameplay to be done. But one of the main feature I liked is because with this mod, one finally could create a three-weapon class by design. Similar to some other certain games (ref: Gears Tactics).

For example, my format of game data are as follows

I took LW2 classes from this mod:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1335226018

(Optional) You may created two custom classes called "Sidearm A/B" (for non LW) and "Sidearm LW2A/B" respectfully with the help of this mod. You do not need to give the classes any skill or stats, even blank works. Just need to assign proper callsign and name with a little description to the class.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1128707437

Now with this, it allows you to have the pistol skill tree on LW2 classes for Favid's LW2 classes mods. Otherwise, you can just assign un-rollable classes such as Rookie, PsiOperative or Spark class
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But it comes with problem when combined with a certain mod to edit the random Xcom perk, aka this mod:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1129770962

The problem with mentioned mod is that it only target the last row in your tree, which means it changed from the XCom random perk tree into the multiclass perk tree instead.

To deal with this, first you need to "take off" your multiclass in any way. But simply assigning like an empty multi class does not work. So comes the help of this mod:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1370543410

With the added command "RebuildSelectedSoldierClass". It will cut out the multiclass row, along rebuild the character however which removes all sorts of it's stats bonus (Welp, that is bad). So better take note of your characters stats before rebuild.

Once you are done recreating the ideal soldier of yours with the editor, you can reassign multiclass to the same soldier. However, this is the another bug: There is still traces of previous multiclass on the soldier, thus you can not reassign the same class. The solution is to make a same multiclass, which is why the twin class added, eg: "Specialist A and Specialist B" with completely same perks.

Now, combined with the utility sidearm extended, add a bit more utility slot and you can have pistol for everyone as sidearm properly.

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PS: Tbh, why this mod has to extract information from original or existing classes? Instead if one could just create a name slot with icon assignment and description wouldn't that be easier for customization?