Maybe I'm doing sthg wrong, but it doesn't seem possible to change my iron sword to a diamond sword. Am I missing sthg or is this a bug?

Side Question: How exactly do you improve integrity? And what exactly does the "!1" mean next to the Craft Button?

Ah okay, so you always need a Hammer in your Inventory to upgrade tools? ^^

Then maybe another suggestion, just in case, that would be easy and possible, I have the mod Improved Backpacks installed, and was wondering if it would be possible to check the backpack inventory too for the Hammers, since I mostly carry them around like that.

Also, big thanks for this mod, and for your quick answers and help ^^

Sort of, some variants or parts requires an axe (and leather/cloth will probably require a cutting tool soon). Supporting tools in backbacks is a good idea, I've been meaning to add support for using tools in the toolbelt as well. I've created a separate issue for the backbacks #16, so I'll be closing this one.