Preserve registrant data on editing a series

[campbell-m]

At the moment editing a series causes registrant data to be lost (although a warning does pop up). That's because if you change the time or date then the system can’t know which slots in the new series correspond to which in the old series. For example if I change the day from Monday to Thursday, should this Monday’s or next Monday’s registrations appear on Thursday?

However if the time and date are not being changed and only something like the description is being changed, then the system should be clever enough to recognise this and preserve the registration data.