I’m creating a character that can change their appearance, this will be a default character for all NPCs and player characters so it needs to be able to swap out face/hair/clothing/armor etc.
Currently I’m working with an idea that you have multiple skeletal meshes, the body, the clothes, the armor, etc. and then drive them all with “Set Master Pose”. Is this okay? ideal? or is there a more efficient way to achieve this and could you provide a tutorial link to it.
pic attached for reference
Well to put things into context.
Character design using components is a worth while consideration as it allows the use of the same base assets on as many different characters as you wish as well makes quick work of making a fair number of different characters using a limited number of fixed assets like clothing, hair and accessory items like helmets and armour.
Directly relating to your question the master pose component is available, of note, to the character blueprint so that the targets will inherent the animation behaviour, in this case from the body, with out having to add the animation asset directly to the component, and in turn creating sync problems.
In form this is how we more or less construct the components of our player models as some assets are are are not required based on the unique requirements of the player model as determined by the class set up via the player customization menu. For example the player might decide that their player will not make use of a helmet or armour so used in game can be flipped so the items are excluded when the character is spawned.
Of interest the Paragon character makes us of more or less the system as well as MetaHuman and Genesis 3/8.
So to confirm yes your theory is sound and in my opinion is a very efficient way to base component character design that would take into an assortment of considerations even before you get there. 
Personal opinion wise UE4/5 takes to modular design like a duck to water so whats important is not the construct of the blueprint, as it’s just a wrapper that supports the asset requirements, but the number of different assets components that are designed to work with in the same implantation channel. (IE all SK assets sharing the same rig and animations)