Not sure I follow, but if you are asking whether the Accountants Edition can post directly to linked accounts, then the answer is Yes it can.

If you mean can you adjust the balance, yes but you usually should not.

If you mean, can you adjust the USD without adjusting the CAD home currency balance, in the A/P account, I have not tried that, and don't have the Accountant's Edition handy to see if it's possible to post a transaction directly to that account in USD with an exchange rate.  

At any point in time except as of the last transaction / end of the last fiscal year, you can have balances that are not zero. If the two are cleared against each other, this is true anytime after the payment.

(If you have a foreign currency payable and a credit note with two different exchange rates, for example.)

If the company file is still in Historical Entry Mode, or if adjustments to the linked G/L account have been made (using the Accountants' Edition) it may not / may no longer agree to the aged A/P detail listing.

I couldn't say, without four reports exported and assembled in Excel:
detail G/L A/P listings showing running balances:
- in CAD and in USD side by side,
- One first sorted by date, and another sorted by transaction number.

You should be able to see where the average USD:CAD changed / went wrong.

Normally there is an automatic foreign currency adjustment posted with each payment, so you could run that listing as well.

This is exactly what i would like to do - adjust the USD without adjusting the CAD home currency balance, in the A/P account. Is it possible ?. I have traced the error to the input of invoices for a customer who's account is in USD, somehow few of the invoices have been recorded as a CAD currency (which I don't have a control, when customer account has USD currency set up it is impossible to change it), when checked in the A/P the outstanding balance was registered as USD, so when invoices ware paid, it deducted CAD currency from A/P leaving USD,
at the end all invoices ware paid but there is inconsistency between currencies. I'm able to adjust CAD but not USD without loosing all the record of the A/P. I don't now if it makes any sens but that's how I see it. Any idea?

JAM48 said:

I have traced the error to the input of invoices for a customer who's account is in USD, somehow few of the invoices have been recorded as a CAD currency

As far as I know, it's impossible to change the currency after any transaction has been posted.   Do you mean that the customer account was set up and billed as (for example $1,300 USD instead of $1,000 USD for goods that would sell for $1,300 CAD, and the customer later paid the correct amount of USD - $1,000?   

This is what I would do:

1.  Make a backup.   There's nothing worse than ending up worse off, or with a bigger mess than you started with.

2.  Restore the backup to a separate, temporary company.    Figure out what you need to fix, then try it, and write down what you do at each step.   (you'll also have the journal entries in the temporary company to refer to)

Don't try to adjust the CAD balance of the A/P G/L account by using the Accountants' Edition to force in a General Journal entry, unless such transactions have already been posted in the past.   If so, find what they are, and either automatically (click the X) or manually (post the opposite) reverse them.   (To find them, run a General Journal Entry (only) report in a copy in Quantum, if the books are Pro or Premium) and search for the A/R account number with control-F).

Find the invoices that were posted with the wrong amounts, and the payments.  

Reverse the payments, then Reverse the invoices.

Now, record the invoices as they should have been recorded, then record the payments.

Or is this all in a long past fiscal year that you can't access?