Leanne.
There have been 16 ft skiff rigs fitted to RL24s successfully, but, the 16s are a restricted class and the rigs do vary in dimension.
The full number one rig on a skiff is 22 square meters and that is two square meters more than the the 24s, so unless you get a small headsail a sail would need to be reduced in area.
This is how I would tackle the issue. Draw up the 24 rig to scale using the dimensions in rhe RL24 class rules on this site, then superimpose a scale drawing of the proposed skiff rig on it with the boom heights level. The main things to watch are the overall rig height and the shape of the foot of the head sail, it will be obvious that the bottom of the mast will need to be shortened and the shrouds and forestay lengths extended, also the spreader angles and width may need to be adjusted.
The full skiff spinnaker is much too large to be considered, and please ensure that the area of the working sails do not exceed the class rules.
