I didn't find any rest API endpoint able to perform this update so, I'm afraid this will not be possible unless you change it directly on the database (wich's not advisable), in fact, Bamboo currently has a bulk action to change triggers but it replaces the current configuration.
The only way I can think of is if you decide to manage your plans using Bamboo Specs (available on Bamboo 6.0+), this will allow you to change any configuration for your plans just editing the specs source code.
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