I'm hoping with fibre an ISP change would require no work from my end - no even reconfiguring my router.
Depends what RSP you are changing from / to - each have different authentication methods, and different settings regarding VLAN tagging
Bigpipe, NOWNZ, Skinny use PPPoE without VLAN10 with no unique username and password - So you could Churn between these with no router Change
Vodafone, Trustpower, Orcon, Slingshot used DHCP with VLAN10 Tagging on - So you could Churn between these with no router Change
Spark, 2Degrees used PPPoE with VLAN 10 - Tagging on (however 2degrees is a unique username and password) - so you could Churn from 2degrees to Spark without a router change, however if your churned from Spark to 2degrees you would need to update your router with your unique username and password)
if you switch from a RSP that uses a different authentication method from your current RSP your router will require a change/reprogram