You don't. An item is either modable, or it isn't.

The exception to the ruie is augments. You can add an augment slot to almost any weapon or armor piece, though if it isn't already modable, it would be a waste of a slot kit and credits to do so.

You don't. An item is either modable, or it isn't.

 

The exception to the ruie is augments. You can add an augment slot to almost any weapon or armor piece, though if it isn't already modable, it would be a waste of a slot kit and credits to do so.

You need to use a modification station to add an augment slot. You can find stations on fleet, in the Strongholds & Crew Skills area, and also on many planets.

Right-click the station, and select the piece you want to augment. There will be an Add Augment Slot button at the bottom. Click that and you will get a droplist of Kits, and the cost to add them. Click the one you want to add and then the Buy Augment Slot button.

Once you've added an augment slot, you can add or remove augments, the same way you do with other modifications (including without needing to use a modification station).

You have to have:

1. An Augmentation Kit - These run from MK-1 through MK-9 and are consumed on use.
    
   Each MK-# has a certain max level of augment that can be used in them. So an Augment Kit MK-1 couldn't 'hold' a Level 55 Augment. But it does work retroactively, so an Augmentation Kit MK-9 can hold a Level 11 Augment.
    
   
2. An Item Modification Station - These can be found on the Fleet, Capital and Starter Worlds, and can be purchased for placement in Strongholds.
    
   
3. Credits - It costs money to install an Augmentation Kit into an item.
   

With the item you want to add a Kit to and the Augmentation Kit in your inventory, you click on the Item Modification Station. Find the item you want to add the Kit to from the drop-down box at the top, then in the drop-down box in the lower right-hand corner, click on the level of Augmentation Kit you want to install.

A few tips related to this:

• Unless you're swimming in credits, it's not really recommended to add Augmentation Kits to gear as you level. It's an extra cost without a great deal of added benefit, since the gear you can get while leveling is sufficient to get past the content and you'll just 'level out' of it.
   
  
• It's also not recommended to add Augment Slots into anything but moddable gear (Orange or Purple with mod slots), since you're likely to junk any unmoddable gear you overlevel or want to replace.
   
  
• Augmentation Kits do not work on a progression. You don't need to start with an MK-1 and upgrade to an MK-2, MK-3, MK-4, etc. up to MK-9. You can go straight to an MK-9, if you can afford it.
   
  
• If you are going to Augment your gear despite the recommendations not to (say, you have Orange gear you know you want to keep all the way into endgame), go for the highest Augmentation Kit available to you, like MK-9. Sure, 36K is a lot to add an Augment Slot for a Level 10 character, but you'll be able to use it for any Augment in the game up through level 55.
  

• If you are going to Augment your gear despite the recommendations not to (say, you have Orange gear you know you want to keep all the way into endgame), go for the highest Augmentation Kit available to you, like MK-9. Sure, 36K is a lot to add an Augment Slot for a Level 10 character, but you'll be able to use it for any Augment in the game up through level 55.
  

Adding all the Kits from Mk-1 through Mk-8 would cost you a total of 102,500 credits - before you pay the 36000 dredits to add the Mk-9.

Of course, getting the MK-9 kit itself will be pretty expensive, especially for a low-level character. But like adding the slot, in the long run it will likely be far less expensive then buying all the MK-1 through MK-8 kits as you go along.