Absolutely stymied on last two - and fear a "wrong 'un" 19d. Doctor in case journalist harassed (8) COMBATED (MB in COAT + ED) If correct: 26a. I'll see if it changes him (6) *B*L*E
20a. I see central theme in long poem, which is conclusive (11) (E?)*I*O*I*T*C I am so far from getting this last one that I fear a previous error. The long poem is, presumably, EPIC
Confirmation and explanation, please. 24a. Pointless emotion (4) *O*E (Love?) 26d. Stir - it could cooler (4) *A*L (Jail, or Gaol - or does it matter?)