okay in like 20 minutes i'm going on my computer to help you
i don't think you can actually overwrite default addons. i've tried it before and it didn't work, for me at least. no matter what it's always better to just make a new one.
first and perhaps most importantly i advise that you make a seperate server.cs. Right now the sword's server.cs handles both server-sided stuff just to make the sword activate and appear in game and also have all the coding (model, attack speed, etc.). This is common for old addons.
Basically, make a "level1sword.cs" and a "server.cs". The name doesn't matter for your sword. If you want to take a look at how to make a server.cs, look at GunsAkimbo's server.cs.
just rename all of the datablocks to your liking, and don't overwrite any.
if you need any help PM me or RTB me ingame "Gumba Jonny".