Received answer from Support:
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I understand your concern that you want to change YouTube Account for uploading video through PowerDirector 12 software.
In regards to your concern, PowerDirector software don't have option to change the YouTube Account.
For workaround, please follow the below steps:
a) Login your YouTube Account directly which you set in PowerDirector
b) Change the Password of Account
c) Now open PowrDirector and try to Upload video on YouTube
d) Because you already hanged the Password of YouTube Account, PowerDirector will show Username and Password Invalid
e) Now from here you can change the YouTube Account
f) Enter your new YouTube Username and Password
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Not as bad as re-install