Once the letter is issued, it is generally not advisable to modify or edit its content. To prevent any potential legal or ethical repercussions, the document's integrity and correctness must be maintained. If any inaccuracies in the given letter are detected, it is essential to communicate with the HR department or relevant authorities within the firm to address the matter and seek possible solutions. They can guide you on the necessary steps to rectify any mistakes or provide alternative solutions, such as issuing a supplementary letter to clarify any inaccuracies.