Across:
   1. Core of decency gave way to mercurial variation, and change for the sake of easy change (7 8)
   9. Curiously evenly bonded clays  (5)
  10. Getting back even can e.g. be 15  (9)
  11. They are treated by one restricted by intellectual property rights (8)
  13. Go two hours before midnight, followed by Cinders' heart (6)
  15. 18 down enter writ, changed beyond editing (9)
  17. Cared about being contested (5)
  18. Score from Francis umpire knocked back   (5)
  19. 15 or revived "Top Gear"? (9)
  21. Observant sowing, once 28  (6)
  22. Prove set play can go too far (8)
  25. Arm up choir? Britain a 9 creature of change (9)
  26. Former Vietnamese president hit EU with upheaval (5)
  28. Reality dawned as 1 across introduced (3 5 7)
Down:
   1. It dispenses with proper motions after death (7)
   2. Rascal in a panic - a dim person? (3)
   3. Month by bed, once 28 perhaps (5)
   4. I violate NT orders during suspension (10)
   5. Colourful name - 8 part of your framework (4)
   6. Got back into dreary Eaton P.E. gear, returning 9 (9)
   7. NT conspired with relocation - unremarkable (11)
   8. Gave up, decidedly 15 without CD (7)
  12. Village folk's pope: "Let's own the means of production!" (11)
  14. Lacking a certain culture since Roo left, worked lone endeavour (10)
  16. In 1 across I've got motivation (9)
  18. Confused single female feline put in inappropriate role (7)
  20. Explain former lover: "That was before 1 ac.!" (7)
  23. Brief reasoning of judgement - read this, or 9 (5)
  24. A bit of chain around the cooker (4)
  27. Rascal in a panic - a dim person? (3)