I have a suggestion for your consideration re: the XPGT margins option.
The scenario is for a retail epub (minus DRM) which has a .xpgt file and has no need for a calibre epub-epub conversion. The epub will either have:
- margins in the .xpgt plus margins in the epub .css
- margins only in the .xpgt
For the former I can see that you would want to remove the .xpgt margins completely.
For the latter, if you remove the .xpgt margins, you would end up with no margins at all, which can be rather cramped on the device. In this case it might be nice to have the option to set .xpgt margins to match those specified in Prefs - Common Options - PageSetup. This should result in the same page margins you would have got if you'd done an epub-epub conversion, but without the conversion 'risk'.