If you assign a number to a field you aren't using (say Tally), with 1 meaning this is a boat/helm to be included in all races, and 0 means they are to be excluded from the overall series, you can then use the set competitor field (in Tools) to exclude those with a 0 in the Tally field. Then (re)score for the overalls. Of course you have to then un-exclude them for the next race.
It does mean that on publishing, the individual races are separate from the overalls.
Depending how you have your scoring set up (long series or championship) scores for DNC, DNF etc will change. Make sure that's what you want.
Of course you can be more sophisticated & use the 0/1 digit field to indicate which races an individual should be excluded from.