It is possible to handle this with Odoo.

Step 1: to create new VAT codes

First one is a duplicate of the standard 7.7% on Sales rate and then to (1) remove the account for the tax, (2) to change the tax grid and (3) to tick that this tax will affect the base of subsequent Taxes (advanced options tab). Please don't forget to do the same adjustment for the credit notes

The 2nd one is for the specific VAT rate you are subject to (4.3% on above description)

1: specify the specific VAT rate

2: 100% of tax goes to the VAT payable account and -100% of the tax (in order to have a debit) comes as a decrease of revenue

3: To mention a tax grid only for the VAT payable line

Step 2: Once both tax codes are created, you need to make sure that the first tax code created (7.7%) is above the 2nd code on the tax code list (as below). You just need to click on the two arrows icon to move them

Step 3: Then you need to create a tax group for both tax codes so the VAT mentioned on you sale invoice remains standard

Now, let's create a sale invoice for 100 CHF (VAT excluded) under this specific regime

As Taxes, I selected the group of tax I created. As we can see it looks like a standard invoice for my customer (100 CHF VAT excluded, 7.7% VAT, total 107.70 CHF)

But let's check the journal items of this invoice

As we can see, the revenue = 107.70 CHF (both on accounting and VAT report). The VAT to pay = 4.63 CHF = 4.3% of 107.7 CHF (revenue VAT included). There is a decrease of revenue for 4.63 CHF. And the total booked on my debtor remains 107.7 CHF

Let's check the VAT report

As we can see, total revenue = 107.70 CHF and total VAT to pay = 4.63 CHF (4.3% of 107.70 CHF)