actually, i just tested the schema changes solution above; editing a ticket updates the created time.  this is because, essentially, editing a ticket performs a DELETE then an INSERT, so the default CURRENT_DATETIME gets evaluated fresh again.  (i confirmed this by inspecting tkt.c [98960a5cdc].)

i'm not sure that the OP's request can be resolved without writing some fossil code.  i'm going to try a few more things with the ui to see if i can get the desired result, but i don't have any more time today.