Am I able to rename my plot?
Yes. If your plotter didn't finish the plot, you are able to rename the plot avoiding the error: "file (file name) name/size mismatch." By doing this you are moving the end of the plot down to the last plotted series of nonces. Skipping any nonces not plotted.
You just need to keep in mind that the new number of nonces still needs to be a multipliyer of the stagger. If you want to be sure you are doing it right, @blago deveolped PlotsChecker to rename the plot for you, without you needing to do anything.