I am adjusting my voltage range to go from 0-1V by connecting the aref to the 5V pin through a series of resistors.
Can I just change my sketch to adjust for the new voltage range or do I have to change change the .cpp file in the library?
Can I just change my sketch to adjust for the new voltage range
Yes. You just need a call to analogReference() to change the reference voltage reading.
I am adjusting my voltage range to go from 0-1V by connecting the aref to the 5V pin through a series of resistors.
Series resistors won't really cut it. You need a potential divider or similar.
Most current Arduinos have an internal 1.1 voltage reference source, so you can switch to that instead - it's easier.