IT'S all change at Swire House, where a purveyor of fine crystal and china is having to make way for an emporium specialising in sesame seed buns. But then, that's Hong Kong. Grenley's, the territory's oldest family-owned business dealing in exquisite glassware, is moving out of its current Central address after a stay of 15 years to make way for the Hard Rock Cafe, an eatery acclaimed for its fusion of fast food and fast music. But Grenley's owner Margaret Grenham sounded a defiant note, saying the business would ''rock on''. She added: ''We are sad to leave our present location, but at least we are going back to Prince's Building, where my mother-in-law opened her first shop in the late 1940s.'' It will be interesting to see how the venerable tenants of Swire House take to their brash new neighbours.