The ending of A Tale of Two Cities always brings tears to my eyes, not just because of the poetic beauty but mainly for the selfless action made by Sydney Carton. If it was to be changed, modified a bit, I would definitely make it a bit more joyful.
The scene would be at the guillotine where Carton faces his death, but instead of sacrificing himself and fulfilling the resurrection theme in the book, Monsieur Defarge would come to his rescue. Throughout the book, Defarge has been manipulated and belittled by his wife. At the last minute, Defarge would make an outburst, pleading for the life of Darnay (he doesn't know it is Carton). The plead would be for Darnay to have one more day before his death because this is what Madame Defarge told him the night before. In this way, Defarge is redeeming himself from his past mistakes which ties into the theme of redemption. Defarge's outburst would be met with hostility by the crowd awaiting the death of Darnay, and disbelief from the knitters and the Vengeance. But Defarge would persist and promise that the next day Darnay would suffer a worse fate. This would excite the crowds because ,like animals, they want spilt blood and the more gruesome the death, the better.
Then Defarge would escort Carton back to the apartment, where he discovers the truth. The Vengeance would find out about the plan at this point, after finding Madame Defarge dead. She would make her way after the troupe on their way to England, but she is held off by a crowd dancing the Carmagnole. Defarge brings Carton back to England with the help of John Barsad / Miss Pross's brother Solomon. They succeed, but only with a few moments to spare. In the chaos with the Vengeance following them , Mr. Lorry is killed trying to protect Lucy; the Vengeance also dies. This supports the assumption that the Vengeance is an extension of Madame Defarge because the Vengeance also dies due to her own doings . Then there is a tearful reunion of Carton and the Darnay family, where sweet words are exchanged and they mourn the loss of Mr. Lorry.
Defarge is forgiven by the family for his past wrongs, and the scene ends with a sun rising (represents a new day, new life, new chances for good.)