I wish that were so, alas the wording in the rules is decidely unclear and certainly leaves wiggle room to insist on revising the base fare when changing the routing after the first segment is flown.

Ie they only *imply* this shouldn't happen by virtue of explicitly saying the base fare will be revised if changes are made before the first segment is flown and being silent on that for when after the first segment is flown. Alas silence is not clarity, cf they are also silent on charging the difference in taxes which we know/accept happens.

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