its not possible to rename the incoming file but u can rename the previous file recieved
Code:
on 1:DCCSERVER:Send:{
  if ($exists($findfile(C:,$1-,1) == $true) {
    var %file = $findfile(C:,$1-,1)
    var %ext = $right(%file,4)
    var %file2 = $remove(%file,%ext) $+ (1) $+ %ext
    rename %file %file2
  }
}

while (demi == nub) {
inc %skill
}