Changing the underlying data structures is usually a tricky job. And I am glad to report that we have finished this feature to satisfaction. So here comes -
you can now create an invoice under multiple account heads (thats what we call). For those of you, who use Mulberry like a straight forward invoicing app, you will not see any changes (except the logo will not appear in the printable format yet.) If you want to use this feature, go to "Admin > Settings". Look for "Accounts". You can add a new account, or edit the current one.
Importantly, even if you don't use the multiple account feature, you can set a prefix for your invoice numbers and set the sequence number from which you want to start the numbering for your invoices.