@robertkeizer What do you mean by 'relative path'? The import statement is
from MQTTLib import AWSIoTMQTTClient
How do you point this to another source?
I added my own copy of the library in the directory AWSIoTPythonSDK, and then was able to use from AWSIoTPythonSDK.MQTTLib import AWSIoTMQTTShadowClient or similar.
Effectively just add your own copy of the library and then use a from xx import ; As long as you don't use the exact same name as the default one, and the directory exists in /lib you should be able to use another version.