Changing a recurring contribution with multiple line items
The 1.6.x branch of the iATS extension is using contribution repeattransaction API -> to get the details of the contribution and its line items that need to be repeated; 

If a recurring contribution has lineItems associated with it - we don't allow updating it in the GUI:



You can (as you noted) update this in the backend -> however -> repeattransaction API will continue to use the lineItems associated with the first contribution in a recurring series as the 'template'; 

Best solution in this case is to start a new recurring series -> with both the correct total amount and the correct break down; Two ways to do this:

1) ask the donor to initiate a new series on an online contribution page; 

2) since you have the iATS customer token -> you can use phpMyAdmin to set up a new series - and attach the token to this. It's tricky in that you will need to touch a number of tables -> and possibly bookkeeping entries as well (if you care about those);