23A - How to make Bank Accounts subtab read only, under Payments tab for Supplier Manager role

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We had cloned seeded Supplier Manager role and realized it allows user to "edit" Bank Accounts added under Payments tab under a Supplier Site. This is a risk for us given anything related to setting/editing Bank Accounts are restricted to a specific business team, so we tried to remove privileges but couldn't find a way to do this.

The privilege is at "Payments" tab level and it seems either user gets the entire area (with 3 subtabs - Payment Methods, Bank Accounts & Payment Attributes) or nothing at all. We then went (the absolutely dreaded) Sandbox UI Customization way but here too, we could not find a way to make only "Bank Accounts" tab readonly. This means Supplier Manager can't enter the "Remittance email" anymore under "Payment Attributes" either.