Can a witness statement I gave Maltese police be corrected later?

Yes, it is generally both possible and appropriate to correct a genuine factual error in a witness statement you previously gave to the police, since the goal of the criminal justice process under the Criminal Code, Chapter 9 of the Laws of Malta, is to establish an accurate picture of events, and a witness who realises they made an honest mistake is expected to clarify this rather than simply letting an inaccurate statement stand uncorrected, provided the correction is made honestly and promptly once you realise the error, rather than appearing to be a strategic change made much later for other reasons. Contact the investigating officer or police station where you gave your original statement and explain clearly that you want to correct specific details, being precise about exactly what was inaccurate and why, ideally documenting this correction in writing or through a formal supplementary statement so there is a clear record of both your original account and the correction. If the matter has already progressed to court proceedings and you may be called to testify, it would also be worth mentioning this correction to a lawyer, since how and when a witness statement is corrected can sometimes become a point of discussion during questioning.