If I buy a return ticket (saver or flex) now, and then modify the return flight (date) in the future, does the (potential) repricing only apply to the return leg component, or does it affect both outbound and inbound? (And worse still, does it then decide "Sorry, not savers now, only flex, outbound and inbound"?)

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Can the outbound leg of the ticket be upgraded after purchase, and still hold if modifying the return leg as described above?


Thanks in advance to the great minds here - hopefully a simple (and not frustrating) answer is forthcoming to slow my hair loss.