Up to two answers per day for the first two days, please 
Bait and switch: Each clue below can be answered by changing one letter in the given, capitalized word, and then anagramming the letters. Some easy, some tough, some may be alterative spellings, hyphenated or Britspeak, and there may be the occasional two word answer...
CERTAIN-1. Very old
2. Italo-Norman leader of the First Crusade (approx 1100 BC)
- best to use Google -3. Storage unit
-4. Area of dead tissue caused by obstruction of local blood supply
-5. Watch manufacturer
-6. Frenzied, agitated
-7. Any inorganic salt containing the univalent group -NO
3 -8. A portion or instalment, especially of a loan or share issue.
-9. European car manufacturer
-10. Part of a set of bagpipes
-11. Poisonous member of the buttercup family
-12. Part of a mosque
-12. Approximate
-14. Rope used for fastening a boat
-15. Crimson or purplish-red colour.
-16. Greek wine flavoured with resin
-17. Hypnotic states
-18. Mythical creature, half man, half horse
-19. Toxic metalloid element, atomic number 33
-20. Disavows, withdraws (a statement, belief etc)
-21. Tank for the storage of water
22. Part-exchange -
hyphenated (5-2)-23. Written composition on a subject, usually in magazines, newspapers etc
-24. Light, semiautomatic rifle
-25. Of, or relating to, suet or fat
-26. In, at, or near the middle
-27. Musical performance, usually by a soloist
-28. Keeps possession of
-29. Hanging piece of drapery
-30. Ungrateful person
-31. Unstable, unpredictable
-32. Clothing, attire
-33. Igneous rock
34. Informal conference, especially on a topical subject, usually held at a university-
hyphenated (5-2)-35. Landscape
-36. To have reference or relation