Depends on the NOR.  If the entry is the boat and there is no other constraint on the person on board beyond RRS-required club or MNA membership then one warm body is as good as another.  But I'd bet that is not what the OA intended.  :-)

Firstly the RRS themselves don't refer to, or place any  restrictions on 'skippers' or 'helmspersons'.  The only reference to such a person is in RRS 46 PERSON IN CHARGE

A boat shall have on board a person in charge designated by
the member or organization that entered the boat. See RRS 75.

Nothing in this rule restricts changing  the person in charge either during or between races.

Any restrictions on changing the person in charge or helm need to be stated in the Class Rules, or NOR or SI.

Haydn .. most short-handed events that I've seen expect that people will be doing multiple duties.  They are defined locally more commonly as "double-handed" where typically these 2 people are racing a boat normally crewed with 5 or more.

John brings-up Class Rules .. that's where "who can drive" rules are commonly found.  OA/RC's should be careful if the short-handed event is being done in One Design boats with a OD fleet-start, that driver-limiting rules are looked for and maybe changed, with a Rule 87 letter from the Class, to accommodate the intention of the event.

Thank you for the helpfull advice and information. Much appreciated