As long as the 24th fret you are looking for is 1/4 of the total scale length [measured from the nut to the bridge saddles] from the bridge, your guitar neck will play in tune. This means, in all likelihood, that the extra 2 or 3 frets you are looking for will have to reside on an (unsupported) fingerboard extension if you want to retain a 25.5" scale length for the re-necked guitar. Ebony is brittle and may not like being unsupported over the extra distance we are talking about for frets 22, 23, and 24. [Violin fingerboards are unsupported over greater distances, but arc-shaped cross section and lack of saw kerfs to accommodate fret tangs, so they are stable and produce good tone.]

The bottom line is this: whatever the number of frets your replacement neck may have, it has to have frets that are spaced approximately 1/18 of the distance of the open string apart. Of course, 1/18 of the remaining scale length when the string is fretted at the first fret is less than 1/18th of the open string, which is why the frets keep on getting closer together as we go up the neck. At the high end of the neck, frets that are too close together can cause more problems than they are worth...

Theoretically, you [or Warmouth] could make a neck with 24 frets [with useable high-fret fret spacing] to the end of the neck pocket, with no fingerboard extension, but you would end up with a total scale length for the re-necked guitar of more like 27" or 28" than 25.5"...[ 28" is getting into baritone territory]. It's not as simple as just firing off an order for a 24-fret neck...

Hope this gets you on your way to an answer.

Regards,

JellyWheat