With Reassign Material ID, the Material ID of the corresponding voxels in the structure is changed. In the example shown below, the Material ID 02 is reassigned to the Material ID 01. No voxels with Material ID 02 remain in the structure, and it is not possible to distinguish which fibers belonged to which ID (01 or 02) after the reassignment.

With the additional option Transfer Corresponding Material also the material of the new Material ID is changed to the material of the old Material ID.

Using Swap Material IDs allows to swap the old and new Material ID.

If additionally the option Transfer Corresponding Material is chosen, also the corresponding materials are swapped.