In general yes - easy editability is one of the great things about TASBooks.
To edit a transaction in TASBooks:
Go to the screen where you originally entered the transaction, then enter the transaction number (or sales order number) to recall it.
Find the transaction on the customer/supplier activity, then drilldown and choose edit
Find the transaction on the audit trail, then drilldown and choose edit
Then click to edit the transaction and save it.
There are a few restrictions on editing though, to preserve accounting integrity. For example; if it's sales order, then you can't change it once you've printed/posted it. You have to create a credit note to reverse it.
In some accounts software, the sales order process isn't always intrinsically tied in to the bookkeeping entries. Which means you could print many different invoices with the same number. We've always followed the spirit of the rules in VAT Notice 700/21 on unique invoice numbers. So once you've 'issued' the invoice by printing and posting it, you can't then issue a different invoice with the same number (although you can of course print a copy of the original invoice).
Once issued, the easiest way to correct a sales order invoice is as Scalloway suggests; to issue credit note to reverse it and then issue a new invoice for the correct amount.