No, you cannot.
Only against the cops, you can change the statements before the Magistrate if you can prove that your statements recorded were under threat and torture by the police.
Added: You can if you wish to. However, depending on whose behalf you are testifying, either the prosecution or the defense will use your changed statements to impeach your veracity thus throwing doubt on your entire testimony.
What witness statement, in what case?
yes
On witness's statement to investigators - no. On the usability and admissability of them in court - yes.
the little boy with the ball
The witness might be punished for perjury, altho I doubt it.
A person who gives a statement is called a witness.
Hearsay
Absolutely.
This is hearsay, which is a secondary source of information that is not allowed.
Generally, written testimony is unavailing if the other side does not have a chance to cross-examine the witness. It doesn't hurt to try, though, if that's the best you can do. A notarized statement might be very helpful to establish damages if the other side defaults (does not show up) and you can be awarded whatever damages you can prove.
In some legal systems, the offender may have the right to see the witness statement, but usually personal information is redacted to protect the witness's privacy. The court usually determines what information can be disclosed to the offender.
The most common method of impeaching witness testimony is with a prior inconsistent statement. For example, if a bystander witness watches an accident, she will give a statement to a police officer at the scene. If she told the officer that the traffic light was red, but later testified that the light was green, her statement in the police report could be used to discredit, or impeach, her testimony.