As far as I'm aware, there isn't a way to add more once you start getting the Too Expensive message, you may have to have a custom enchant that has a similar effect.
if you rename the item when adding enchantments to it, it doesnt count towards the maximum levels spent on enchantments and repairing so you need to do that from the start
that sword is cool and all but i recommend killing the mini boss in tangleroots in /worlds. he can drop a golden knight sword which is way stronger! might take a while to get but its totally worth it!
