... and confirmed - the Working Holiday Visa cannot be converted to another visa type (for Australians at least).
The Chinese site at boca.gov.tw/ct.asp?xItem=623 ... e=738&mp=1 has a statement that is not found in the English site:
translated roughly, that's basically:
After entry: Holders of working holiday visas, after entering may not apply to change to other visas within Taiwan.
Linked from this page is:
boca.gov.tw/public/Attachmen ... 492271.doc
which is, surprisingly, an English language document: "Guidelines for Visa Application to the Republic of China (Taiwan) for Australian Nationals Joining the Working Holiday Program". In this document there is a statement:
One reading of this is "if you've stayed more than 180 days, you can't convert to another visa", but more likely it is a translation error and should be read "No changes to visa type permitted."