@Natty-Boh-man Unfortunately, capsules can only be added while affixing a unit. This means that if you've already affixed your base unit, you risk losing everything when affixing again to add the capsule.
To avoid re-affixing the base unit, most people add the S-grade aug to a fodder unit while affixing 100% success junk augs. Then they use the S-grade augment transfer option to move it over to their main unit without losing its current affixes. What makes this potentially difficult is that S-grades can only be added to 13 star units so you need a 13 star piece of fodder. The easiest sources I know are drops you have from Rainbow keys, Novel units from the RWB5 shop, or upgrading a(n Ivlida and then) Cleasis unit into Schvelle using materials from the RWB4 shop.