Read the definition of “rules” (d) the class rules (for a boat racing under a handicap or rating system, the rules of that system are ‘class rules’).
In a PY handicap race the handicaps defined by the RYA are for boats racing in the configuration defined by their class rules. However, the PY handicap can be adjusted by the orgainsers of a particualr event. There is no reason whatsoever why our club should not allow you to sail single-handed, and they have every right to adjust the PY handicap when you do so.
In the same way you could run a Whitesail category for neophytes, with a handicap correction for not using the spinnaker.
It would be a matter of club policy whether you would be allowed to declare on the day of the race that you were sailing single-handed, or if you had to sign up for the whole season. If allowing some flexibility gets more boats on the water then I feel the club should allow this… for handicap racing.