Lego†Miestersaid: I tried mine on and was able to repair it on an anvil from 100% back to tradable (and augmentable) at no cost, thank goodness.
I think you thinking about something else. Custom fit can not be made tradeable just by repairing it and to repair it you need a full set of standard masterwork.
I think they should just let us repair full sets with pieces of lined masterwork plates for around 8-10% each. Its still a long process and bars will still hold the value. Same way as you can equip full obsidian armour and repair with shards.