[MultiWonder]

(DISCLAIMER: This was tested on the Test Server.  I thankfully caught this before trying anything funny on main Dx)

Upgrading a standard yin / yang into their guilded variants does not carry over regalias.
Interestingly, it still marks it at 'Customized and Pristine', when in truth, you can't apply any attack animations to it nor does it wield any re-dos.

[Neus]

This has been corrected in 3.00. When using an upgrade recipe it should retain the regalia, any redos, and an attack style slot (if you used an attack regalia on it).

Note that this only applies to upgrade recipes (the ones that transfer qualities, like gilded Yin/Yang). If an equipment item is consumed for a different item, for example, the new item will NOT retain regalia changes.