Posted No. Series

Hello everyone.
we use dynamics BC14 and we have a requirement to have different posted sales invoice no series than the originally defined one in sales & receivable setup.
we can do this manually buy changing the posting no. series in the sales invoice, but we are looking to automate it by validating the no series initially used in the sales invoice header.
for example, we have below:
1- S-INV for local sales.
2- S-INV-F for foreign sales.
I'm just lost in where to start automating this.