Using SQL Server's 2016 Temporal Tables to Record Prior History
Currently temporal supports system time, which means the date/time values placed in those start/end time columns are populated by the system. 

In a future version, temporal will also support application time, which will provide ways to have the application dictate the time and, I expect, to update existing data with real start/end times.

The only way to override this really would be to archive data from the history table into your own table (which you may end up doing over time to keep the history table from growing forever anyway), change the times there, and use that table as part of your queries.