ORIGINAL: Historiker
I'm going to design my IATB-Series again.
CV-conversions will demand a certain repair shipyard and will be delayed for the correct time while the conversion is done. The HR will be, that the repair shipyard used by the conversion mustn't be used by another ship. The conversion costs will already be reflected in the building costs of the conversable ships as I simply assume they are already prepared.
One might metaphorically think about a Liner that is construced as CVE and then gets the hangar and the deck filled with additional walls, stairs, decks, etc. to make the ship useable and look like a liner. Back in repair shipyard, all the additional things can be welded off at pull linkages. Then the already prepared CV-gear is put in - et voila: a CV(E)...
This will allow the Japs to benefit from bigger repair shipyards and huge conversion programs will block most of the repair space so that battle damage can't be repaired...
(This is no way to advertise my not even existing own mods [;)])
Fair reasoning, and it works for shadow programs and limited conversions. Unfortunately I do not believe it reflects the amount of work in a proper shipyard (which could be building another new CV) to reconstruct one of the old BBs into a proper CV capable of 28-32knots. The only class it might be remotely viable for is the Kongos (or in the CV Variant the Fuji's and Yamato's), as they already have suitable machinery. Anything else is comparable in scale to the rebuilds of the 30s which took several years. It still dosent account for the resources (HI, ect) required. I personally believe the repair yards should have used HI to begin with, to make things interesting...
The rule you suggest about requiring a Repair Yard working on a conversion to not be used for repairs is good, and could be used to replace my '2 CVL/BB and 4 CVE' conversions at a time. A more complicated variant might be a Repair Yard cannot use 'Conversion Requirement + Ship Requirement' tonnage during a conversion. So a 100 point Repair Yard could work on a 15,000t (15 points from ship) CS -> CVE conversion (30 points) and still have capacity to work on 55 (55,000t) points of other stuff. That might be overly complicated however.