[douglas]

There's no restriction on adding or removing stellar manipulation components through retrofits at all, aside from the cost difference limit. This will cost a LOT of resources, though, at least for the last retrofit, as you will be both removing some very expensive components that serve only to bring the ship's cost up and adding the even more expensive final component. The final retrofit can easily cost 100k+ in minerals alone. In the case of a star destroyer, it will be 120k minerals, 60k organics, and 120k radioactives, plus 30% of the cost of the components you remove. This comes directly out of storage before resource production for the turn, though you can also use resources given to you by other empires that turn, and the product of resource conversions. Income from scrapping ships will also be available. It's better just to have the storage, though.