The issue of service within 120 days can be handled a couple of ways. First, if the party you're serving doesn't raise the issue or agrees to ignore it, it will not be a factor. Second, if there's a good reason for not serving within 120 days (like the party being overseas) you can apply to the court for an extended time to serve.
Finally, if none of those works for you, you can always spend the $210.00 for a new index number.
You must apply to the court before the expiration of the 120 day limit in order to obtain an additional 120 days to serve process. With all due respect to my colleague, once the 120 day limit has expired, the case is deemed administratively dismissed and even a stipulation between the parties cannot serve to revive it.