Hi Jaime,
you might have to do that at some point anyway. For example you might have a pending sales invoice in draft which won’t be billed in the end. If you wan’t to reuse that sales invoice ID you can do this by resetting the naming series to that number.
The system will not allow two sales invoice with the exact same ID.
Also you should be able to fetch several sales orders on a single invoice:
will that do the job?
Best
Wolfram