As part of getting to know the CSD Python API and how it interacts with the CSD Python API menu of Mercury I created this simple python script.
It allows you to perform a reduced cell search on the currently viewed entry to see if there are other entries in the CSD that have similar reduced cells, in much the same way that CellCheckCSD does but in a more interactive manner. As such you could imagine loading a work-in-progress .res or .cif file into Mercury and performing this search as part of your initial investigation of the structure. The script will return the currently viewed entry as well as any hits in the CSD so that the current entry can be easily compared with the results.
To use, copy the attached cellcheck.py file to the scripts directory in your Mercury installation, or use the CSD Python API->Options menu item to add the location containing the script. It should then appear in your Scripts menu when running Mercury.