Set up special GL posting keys SD-FI

Greetings,

We have the following Scenario:

I'm creating a billing document in VF01, with accounting document to FI.

Here follows an example of the accounting document:

As is:

We have a requirement where we need to redetermine data when the accounting document is being created.

What needs to be done: the line with account 1105030002 (VEF account), posting key 50 needs to be created with a special GL indicator (@), posting key 19 (required for special GL) and the account has to be the customer's account (2374).

In other words, to objective is to change a GL account (KOART = S) to a customer account (KOART = D), changing also the posting keys (50 to 19) and special GL indicator.

So, the "To be" scenario would be like this:

To be:

****************************************

Questions:

1 - Is there any standard solution which could help us in this requirement?

2 - We have already checked at user-exit EXIT_SAPLV60B_008 but just changing the special GL indicator, posting key, account and account type (D) doesn't work (we have manipulated XACCIT structure). The accounting document wasn't created (Error in accounting interface). Is it a viable/secure option to manipulate the lines in the accounting document by using this (or another) user exit?

We think that changing this user-exit would need several checks/validations/data manipulation, because there are too many uncommon characteristics between an accounting line with a GL account and an accounting line with a customer's account.

Our biggest concern is about conceptual issues which this change could cause. It doesn't seem a suitable option, as we would be doing a deep change in this process core logic.

Any suggestions?

Thanks in advance!

Fernando Demitroff