setting billing date for recurring services and hiding dates

[banar]

Here's what I sent to the support via ticket:
Some clients want to be billed for some recurring services on a specific day. E.g. 12th each month. How do we make sure that for those services clients don't see a changed term they are billed for? E.g.https://d.inco.re/i/Ae2Icvif we change the due date, all the future invoices will have a different term listed next to each service.

So, two questions:
1. how to hide months next to each invoice item
2. how to change the billing date for specific services without changing the date next to each invoice item.

E.g. on 25th each month client is paying for the service for the following month. So, instead of charging the client on 25th and showing "example invoice item - (02/25/2023 - 03/24/2023)" we want the dates to stay the same, be gone completely, or just say it's for MM/YYYY.


Here's what they recommended:
 

WHMCS will always place the period for each service on the invoice. The start of that period will match the due date of the invoice. Unfortunately there is no inbuilt option to exclude the period being listed on the invoice.

However, you could potentially use the InvoiceCreation hook point to run your own code to adjust the invoice line items when the invoice is generated. The invoice could be adjusted by calling the UpdateInvoice API command within the hook.

https://developers.whmcs.com/hooks-reference/invoices-and-quotes/#invoicecreation
https://developers.whmcs.com/api-reference/updateinvoice/

I trust that gives you a good starting point for your customisations/development.