Tamper with a casting, then you'll still have the original with the prepro routes in tact. Plus it would probably be easier to alter on a freshly cast piece as opposed to the original which has already been through a lot.
the dent is a major concern. the previous castings had very dulled dents compared to some of the other helmets out there.
Are you doing a one or two part mold for the next helmet?
Seem lines are also something to think about as the castings from the last run needed moderate cleanup to get rid of the line from the mold jacket