Adding new header fields to EDF files

Question

I have a EDF file to which I need to add some extra header fields. For example, I want to add these two new fields.

header.startFrame=1 and header.endFrame=10;

But when I create these two fields in the header structure, the lab_write_edf from the Matlab EDF library does not include these fields.

Does the EDF file only accept default fields according to the standard?

Also, even if I were able to include the new fields will the edited EDF file be accepted by tools like EEGLAB or WFDB?