Invoice number update manually option

Verzoek

HI we want to create manually invoice in one customer account, but issue is that when we create invoice and put the invoice number and click on paid after that its remove those invoice number which i have put and its take its own series number, so we need the add invoice number manually and paid this invoice , after paid the manually invoice number should not be changed, just because we have lots of reseller and other client which paid by check and transfer and we give them different invoice number