Yes, you can certainly use the checkpoint file for this purpose!
If you are writing scripts by hand, have a look at the manual entry for
restoreSelfConsistentCalculation().
In VNL, drop the original geometry on the NanoLanguage Scripter (to make it understand which system you are using). Then go to the "Self-Consistent Calculation" tab and tick "Restore calculation from checkpoint file", enter the NC filename, and UNCHECK "Only use initial density".
Then, set up the analysis as you would otherwise.