When necessary it can be changed (see response below from USA HOCKEY)- NJYHL should allow changes like the EJEPL does and they should also change their divisions and rankings to allow for better competition like the EJEPL does. NJYHL can do better for our money!!
From USA Hockey:
The general rule of thumb is that once the scoresheet has been signed after the game, no changes should be made as it is an official document recording that game. However, when dealing with amateur officials and volunteer scorekeepers, mistakes are going to get made and some leagues will allow changes to be suggested through the proper channels while others will maintain a hard line and not open up that Pandora’s box as the league administrators are volunteers with limited available time, as well. The bottom line is that it is up to each administrative body (league or club) as to how they want to handle those types of corrections and I would suggest the vast majority do not accept changes unless it involves possible suspensions or it affects the league standings.
If statistics regarding goals and assists are that important to the team, then some coaches will track these things on their own on behalf of the team so they have accurate information for their records.
Best wishes for a successful season!
Officiating Education Program - USA HOCKEY