The basic difference is that leather, studded leather, breastplate, chain shirt, scale, banded, splint and even half plate were always nothing more than a chest (& back) with maybe an attached hip skirt. Chainmail was a headpiece (coif) (maybe with a separate helmet over that). And chain leggings. Plate mail was full chain with plate pieces attached and plate armour was a a full plate exoskeleton. In essence medium and light armours are just the chest and back and maybe hips, so adding a helmet, gauntlets and boots/greaves was always an option but not part of the armor proper. Heavy armors are different in that they include those pieces as part of the standard set you buy - which is part of why they are more expensive. Plate with its many interlocking but overriding pieces actually was so expensive that only the wealthiest or highest in position could regularly afford it (hence the 1500 GP cost). If your DM interprets the rules such that enchanted plate (etc) is created as a full articulated suite for an individual then placed as a unit on the “enchanting table” (the first possible way I covered) then you have to keep the pieces together to get the benefit, you can’t infuse them with other abilities (because they are no longer mundane) and you can’t substitute other found objects in instead of the original pieces of the armor. That is pretty harsh but it’s not outside of RAW because RAW never specifies. On the other hand if the DM rules that only the body piece (chest, back and hips) actually get the enchantment just as with light and medium armors then you are free to add your own mundane or magical helmets, gauntlets and boots - whether enchanted or infused or still mundane. The things you can’t do are: 1) add an infusion to to any enchanted item - even common magic items. (So you can’t use the enhance armor infusion on armor of gleaming to get +1 or +2 armor of gleaming. 2) add the same infusion to 2+ items at the same time - so you can’t put the enhance armor infusion into a plate chest piece AND into a shield at the same time. 3) have your infusions grant a +3 to any item in any way - the best you can do (at L10+) is a +2 to one piece of armor/shield and a +2 to one weapon.
I don’t see anything in RAW/RAI that says that (using interpretation 2 which is basically what is written into the armor L9 ability) to saw you can’t mix a +3 plate body piece with an infused helmet and gauntlets and an enchanted pair of elven boots and combine them into your arcane armor. I will say that as a DM if you tried to bring a L10-16 (or lower) character with such armor into my campaign I would reduce it to a +2 by fiat (or +1 if the character is below L10) as that is too OP for those levels. I might treat it as a legacy item something like a moon blade and allow it to regain that +3 when you reach L17.
The basic difference is that leather, studded leather, breastplate, chain shirt, scale, banded, splint and even half plate were always nothing more than a chest (& back) with maybe an attached hip skirt. Chainmail was a headpiece (coif) (maybe with a separate helmet over that). And chain leggings. Plate mail was full chain with plate pieces attached and plate armour was a a full plate exoskeleton. In essence medium and light armours are just the chest and back and maybe hips, so adding a helmet, gauntlets and boots/greaves was always an option but not part of the armor proper. Heavy armors are different in that they include those pieces as part of the standard set you buy - which is part of why they are more expensive. Plate with its many interlocking but overriding pieces actually was so expensive that only the wealthiest or highest in position could regularly afford it (hence the 1500 GP cost). If your DM interprets the rules such that enchanted plate (etc) is created as a full articulated suite for an individual then placed as a unit on the “enchanting table” (the first possible way I covered) then you have to keep the pieces together to get the benefit, you can’t infuse them with other abilities (because they are no longer mundane) and you can’t substitute other found objects in instead of the original pieces of the armor. That is pretty harsh but it’s not outside of RAW because RAW never specifies.
On the other hand if the DM rules that only the body piece (chest, back and hips) actually get the enchantment just as with light and medium armors then you are free to add your own mundane or magical helmets, gauntlets and boots - whether enchanted or infused or still mundane.
The things you can’t do are:
1) add an infusion to to any enchanted item - even common magic items. (So you can’t use the enhance armor infusion on armor of gleaming to get +1 or +2 armor of gleaming.
2) add the same infusion to 2+ items at the same time - so you can’t put the enhance armor infusion into a plate chest piece AND into a shield at the same time.
3) have your infusions grant a +3 to any item in any way - the best you can do (at L10+) is a +2 to one piece of armor/shield and a +2 to one weapon.
I don’t see anything in RAW/RAI that says that (using interpretation 2 which is basically what is written into the armor L9 ability) to saw you can’t mix a +3 plate body piece with an infused helmet and gauntlets and an enchanted pair of elven boots and combine them into your arcane armor.
I will say that as a DM if you tried to bring a L10-16 (or lower) character with such armor into my campaign I would reduce it to a +2 by fiat (or +1 if the character is below L10) as that is too OP for those levels. I might treat it as a legacy item something like a moon blade and allow it to regain that +3 when you reach L17.
Wisea$$ DM and Player since 1979.
Just wear silk armor under... or over your magic armor.