[GNC] How to accurately record Use Tax

[Brandon Captain]

I make purchases for which I owe state Use Tax on. It's important for me to
record the Use Tax liability at the time it becomes a liability, but only
record it as an expense at the time that I pay it.

I have several accounts for this, but the important ones are:

* "Future Expense(A/P):MI Use Tax", a top-level Accounts Payable account.
* "Expenses:MI Use Tax"
* "Liabilities:MI Use Tax"

When I make a purchase that I owe use tax on, I make a split transaction:
* decrease an asset account by the amount I paid, and increase the expense
account by the amount I paid (not including the unpaid use tax).
* increase the "Liabilities:MI Use Tax" and increase "Future
Expense(A/P):MI Use Tax"

In the next year when I remit the Use Tax to my state, I create another
split transaction for the amount I pay in use tax:
* decrease whatever asset account, and decrease "Liabilities:MI Use Tax"
* decrease "Future Expense(A/P):MI Use Tax", and increase "Expenses:MI Use
Tax".

This method allows me to keep the Use Tax that I pay recorded in the proper
year - I can't record it as an expense at the time I buy the item, because
I haven't paid that portion of it yet, and I don't want to have to remember
that come next tax season.

I am not using the default "Liabilities:Accounts Payable" account because
it would negate "Liabilities:MI Use Tax", and would always look like I have
a zero tax liability which would be incorrect.

So this setup seems to work, but I'm unsure about the GnuCash documentation
which says: "Transactions involving an Accounts Payable account should not
be added, changed or deleted in any way other than by using post/unpost
bill/invoice/voucher or process payment"

I don't use the payment system (yet), but why is it such a problem to
manually enter A/P transactions?

Is it really that important that I use the bill/payment system for these
transactions? And once I do so, can I safely split them afterward?

Thank you