You have a number of alternatives:
- Open the model in a 3D-editing software and change the path.
- Open the model with notepad (or any other text-editor) and find and replace all paths.
- Write a program that takes a folder or file-set as argument and let it do the work for you. (This is good if you run in to the same problem with another project)
- Find a program someone else has already made for this.