Custom portal theme updated by SP upgrade

We had built a custom theme and set as default for quite some time. Recently, our SAP portal was upgraded from 7.01 SPS4 to 7.01 SPS8. Since then we found that the appearance of some webdynpro abap applications (some from SAP and some are custom built) were changed. In portal display, we found that some new elements were added to our custom theme, e.g. Page Header, and which affected the WDA appearance.

Will portal custom theme updated by SP upgrade? If yes, what will happen to custom theme apart from adding new element? Will setting of existing element be affected? Should I manually update custom theme to fit our needs?

Thanks.