The phrase "substantial changes" refers to significant or important modifications that have a notable impact or consequence. These changes are not small or minor, but rather considerable and substantial. Full definition
The court will need evidence of substantial changes in the lives of either party before a modification of divorce decree provisions is issued. (info.legalzoom.com)
A parent seeking the modification of a current custody order should be prepared to present proof of a material and substantial change of circumstances. (thespruce.com)
Although the government tries to regulate product safety, it is people who have been injured by products that have made substantial changes in how products are designed and manufactured. (hepworthholzer.com)