The short answer would be Temporal Z-Space Tethering (+1 to Aluminator for his input. It just got me out of this situation!
)
When you morph a subject that contains more/less mass, the nanites are gathering that mass out from Z-Space and keeping it tethered to you by maintaining a bridge across space-time, only capable of maintaining such a bridge for 2 hours at a time.
If you were to attempt to morph, say, a friend with gold piercings
everywhere, the mass used for the piercings would be sent back to Z-Space upon demorphing.
Not to mention that unless you've actually
had those piercings or
are a piercer, it would be a little difficult to correctly place those piercings (eg. You would have off-centre labret or septum piercings).
As for
demorphing into clothing or with piercings, with the spandex, the subject is creating that from their
own bio-mass. They're litterally converting their own skin cells/muscle tissue/ etc into the spandex that they would need to wear. Because of the form-fitting, lightweight material that spandex is, they aren't actually sacrificing a great deal of bio-mass to do this (barely 1-2 kilos/pounds ... I know they're different weight measurements, but I'm trying to focus on one science at a time
), the same with jewellery.
As for loose fitting clothing that can be morphed
much later, they're still sacrificing their own mass to do so. Depending on how healthy the subject is, people will just think they're looking a little leaner lately.
In other words, if the subject were to demorph gold jewellery onto their body, they would essentially be selling off their own body to do so. Kind of like a tit-for-tat,
quid pro quo, Equivalent Exchange rule.
So, it's relatively plausable, but you would have to posses that certain mind-set that would cause you to sit back and think "I'm going to go sell pieces of my body to make ends meet."
It's a little bit different to giving blood.