Remove text from columns that may or may not be present multiple times
Something like this?

UPDATE dbo.OrgUnits
SET OrgUnitName = RTRIM(REPLACE(OrgUnitName,'('+OrgUnitKey+')',''))+' (' + OrgUnitKey + ')';


View the result

SELECT  OrgUnitName from dbo.OrgUnits;


Result

OrgUnitName
Company1 (5)
Division1 (1)
XAVAT (4)
WATe (7)
Communications (05-905-6320-300)
Corporate Development (05-955-6320-300)
Corporate Board of Directors (05-111-3515-301)