How do we change the mount point for the local space?
could you specify in the context of which node or task you are asking us this question?
Maybe you find this guide useful as it explains pretty well how to access different file systems from within KNIME Analytics Platform: KNIME File Handling Guide.
If you look into the different options on how to access the data, you see that with the Mountpoint option you will be able to specify a mountpoint ID: such as LOCAL, your KNIME Server mount points, if any, and the KNIME Hub.
If I correctly guess what you are trying to achieve, you might be interested in a Relative to option, which would allow to specify Current mountpoint. In this case, the working directory corresponds to the root of the mountpoint.
Let me know if that helps.