I agree '- that level loss is too great - what I am trying to emphasize is "downside" of applying ship customization.
Loss of a level is heavy, and was just an idea or example. A Call Leviathan for a failed attribute is not a viable result. Attribute loss is heavy, too. I threw those out as examples.
There's many ways a downside could be applied - for instance, you have a chance the attributes fail - you can plan on 75% of the guns fire on war galleons, but there be a say 25% chance the operate as normal.
I am certain we can generate some ideas that will be more reasonable.