You need to create a new row for it in K1's appearance.2da, copying across the appropriate values from TSL (bearing in mind the differences in columns). I gather you have already done that part.
Then you need to create a new UTC for it. You can do this by duplicating an existing K1 UTC, changing the appearance, giving it a unique resref/tag, giving it appropriate feats, editing the inventory, etc. Look at c_lightsaber004.utc in 907MAL to see what Obsidian did.
After that, you'll need to add it to the module's GIT to make sure it spawns in the module. Depending on what you want it to do, you may also need additional scripts and/or dialogues.