As long as you are consistent and fair with your changes, 4th graders tend to do well with them. I'm a bit partial - I've taught 4th for 11 years. I sort of think it's the most awesome grade out there.
I don't know what state you are in, but in Louisiana 4th is one of our high stakes testing grades. If that's the case, you will want to find out as much as possible about the test and the content you will need to cover. Good luck, and I hope you enjoy 4th as much as me!