where should I change postbitlegacy_userinfo_width?

[Lynne]

You are going to have to write a plugin that does the if statement for you and then set the width in the classes then. You can not set a stylevar like you are trying to do. When a a stylevar is changed via the stylevar editor, it creates all new css files. Changing a stylevar in a plugin does not do that. So, you need to actually change the css at that point which means modifying the classes.