I want to be able to modify for example the attack_damage attribute and save that item in a kit. As of now the attributes do not save over and I would love this to be a feature!

Kits do already have the ability to accept vanilla NBT, which can be used to apply attributes. The /createkit command does not currently have the functionality to read this data, so it must be done manually. The format for using NBT in Essentials kits is as follows:

- <itemname> <amount> {nbt...}

Note that vanilla NBT is incompatible with Essentials meta, so essentials tags like name and <enchantment>:<level> cannot be used simultaneously with NBT on a single item.

Oh thanks!