Me again

This rule has been around for at least four years (looking back through my incomplete set of old rule sheets it was there in a 2012 rule sheet).

So to summarise the rule:

IF the fare has increased and prior to departure you wish to:
- do anything at all to the first segment (even just a date/time/carrier change)
and/or
- change any of the ticketed points
THEN you must pay the fare increase

After you have flown that first segment then you will not have to pay the fare increase no matter what changes you want to make
And of course if the fare has not increased then you have no problems at all