Changing weldment profile inserts library feature instead of changing profile if there are sheetmetal features and other library features in part.
SW is aware of this bug since 2015 and even recorded it. However it is neither fixed nor is a fix to this issue (SPR 644470) posted.
To resolve the issue simply drag the blue bar in the feature manager above the sheetmetal feature und back down.
Thanks to jörg.jwd at OT Info zu Fehler in Schweißteilen (DS SolidWorks/SolidWorks) - Foren auf CAD.de for letting me know.