I will show you with consol commands, how to equip your companion ( or any npc ) with anything you want.

When reading this guide, i assume your already know a bit about consol command, it is not made to explain each command in detail or how "target" / "reference" / "object id" ... work.

• unequipall This command will be use first to be sure the selected npc will not get any "corrupted" information
  
• removeallitems player Here the command will obviously remove all inventory items from the target, and give it to the player
  
• equipitem #id is similar to additem, but do not add more item if one is already present and equip it directly, additem will not.
  
• cf "ObjectReference.AttachModToInventoryItem" #target #id Will allow you to attach a mod to "the first / last" item found or spawned in the inventory.

In most case for your personal usage you may use something like ( va'ruun inflictor exemple ) :
This "bat" will create the weapon, select it in the consol and apply quality and rarity mod to it.

But it won't work when adding stuff directly in an inventory because additem or equipitem do not return the new reference object id.

When you want to edit the item on an inventory you must use :
Of course you can avoid "player." if you first select yourself in the consol ( prid player or 00000014 ), or if you have selected the npc you want to edit.

Again i will not explain in detail each command, a lot of website already explain everything beter than i will.

Also be carefull when adding a mod to your armor or weapon, if you use the help command for long barrel, you will see a lot of ID, because each weapon as it's own barrel mod, only the rarity will work for any weapon :
and for armor :

Go to your starfield folder, and create a .txt file at the same place of your Starfield.exe ( or in custom folder if your wish ).
Place the code inside the file, and in game use bat <filename> without the file extension.
If you use a folder : bat "Folder/Filename".