WesWorld

The infrastructure rules provide for what you seem to want to do here:

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2.2.3 Rebuilds
Although a refit does extend the career of a warship, she will need more extensive work after thirty years of service in order to remain effective. For each year over thirty that the ship has been in commission, she will suffer a 5% penalty to all aspects of her operation (combat, speed, damage control, etc) as parts simply wear out. Note that a ship may be rebuilt at any time, subject to the terms of relevant naval treaties. A rebuild will require that the ship be dry-docked.
It is easiest to state what may not be conducted during a rebuilding: alteration of the ship’s dimensions; addition/relocation of new barbettes; or changes to belt armor.

What is allowed includes removal of barbettes (for replacement with anti-aircraft guns, etc), replacement of coal-fired boilers with oil-fired boilers, installing new engines, replacing the superstructure, reshaping the bow, adding torpedo defense blisters, removing or adding any secondary guns, or replacing heavy guns in barbettes (such as that done by Japan when she converted Mogami to a heavy cruiser). Regardless of what does take place, the ship’s weight may not be increased by more than 20%.

To determine the time and materials required to rebuild the ship, calculate the ship’s light displacement after the rebuilding is completed. The cost in time and materials will be half of that required to build the ship from scratch. Note that rebuilding a ship will also take care of problems resulting from overdue refits.

Once rebuilt, the ship is essentially new again; she will not require a refit for 15 years, nor rebuilding for another 30.

Example: With the defence budget somewhat tight, India elects to rebuild the battleship Gujurat (ex-RSAN Queen Fallatia) in 1932. Her light displacement is 16,413 tons.

The rebuilding includes: addition of a clipper bow, replacement of sixteen casemated 5.9" guns with four twin 5.9" turrets, replacement of the 3.5" guns with 4.1" and 1.4" guns, and new machinery. The work will leave her with a new light displacement of 17,046 tons.

Material required is 50% of that new light displacement, or 8,523 tons. Time to complete the rebuild is (17+9)/2, or 13 months.
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So while you're at it, you may want to also consider upgrading the armament.

I agree with AdmK on this. You have to do a rebuild as per the rebuild rules you´ll find in the infrastructure rules.

Those were, with the exception of the never completed Aquila, not rebuilds, but new-builds. And the present rules do not seem to have anything in them regarding reuse of components.

Unfortunatly that would look like a rebuild, unless you plan on useing them for 10 years i would say scrap em and replace them with new ships or leave em as is. Another alternative would be defering the rebuilds to another nation with a larger building capacity and funding the rebuilds with curency or the eqivilant in merchant ships or smaller warships. Any ideas?