EDFbrowser: writing an inverted signal to an EDF file

Hello, I'm not sure if this is the place to communicate about EDFbrowser, but I will give it a try.
I have been using EDFbrowser for two days now and it works great. Very powerful and it handles large data sets. I have some data sets where the ECG signal has inverted polarity. I would like to correct it and write the corrected signal to a new EDF file.
With this goal, I am able to create a subtracted signal, using the Signals->Add menu option and the new signal displays correctly. Then using the Signals->Organize tool, I can delete the original, leaving only the corrected one. I am then able to save the file. However, when I reopen the file, I still find the original uncorrected signal present, with no sign of the new one. My reason for doing this correction is that some of the files have the polarity correct and some are inverted. I have later processing code (using your excellent EDFlib in python) that read and process these files. But with the variable polarity, it is complicated to use them. It would be handy to correct that polarity in EDFbrowser. Thank you for your help. Best regards, Kevin Shaw