To save Armor Customization without buying spending DC for Customization Catalysts:

1. Open Spider's Fixed Trainer by Shape_Snatch or Jikaronan

2.A Open Customization Catalysts shop (Shop ID 704) and use the Shop Lifter. Get the item you want.

or

2.B Use the item forge and add an item with the name of the catalyst you want. The customization only checks if an item that has the following name is in your inventory.

Consuming Adept Catalyst
Spectral DeathKnight Catalyst
Royal Astravian Catalyst
Marauder Pirate Catalyst

3. Go to Armor Customization portal. Select the customization you want. Then save!

If you really liked the customization, I still recommend you to buy the customization for DC's eventually so that we can have more customizations.

Let me know if this worked or not.