No need to re-purchase, you should be able to re-download the files from the store page or your itch.io library. :D
I may remake the tool UI for this template into something simpler, as the current one can be a bit difficult to use. It was intended as a bit of a placeholder for people to test with and then create their own UIs, since cycling through a million different types of seeds is probably going to get super annoying for the player. You could also use a plugin like VisuStella Button Common Events to have a Minecraft/Stardew style UI:
As long as the "Tool ID" variable is being changed to the one you want to use, the rest of the template should work fine.
If you still really want to use the existing UI, you can add new tools by creating a new "jump to label" command under the ones in Common Event 117.
Follow the pattern of these, but the last one should always jump to label 1. Think of the labels as the UI's "slots" so once you get to the final slot, it jumps back to the first one.
Whatever label is jumped to, the events will then start playing from that point onwards.
So if the player is currently holding Tool ID 4 and pressed pageup to swap to the next tool, the event would check that the Tool ID variable = 4. Then it would jump to label 5, which checks if the player owns the correct tool for that slot. If they do, it changes the Tool ID variable to 5.
I hope that makes sense!