There are two ways for administrators to shut off the bot:
To disable edits by the bot, remove 'go' from User:WelcomerBot/Run. Please note that this page is reloaded after each edit, which means it may take the bot as much as one edit before it stops.
In case of extreme malfunction, and if the above method doesn't work then block the bot. Make sure you turn autoblock off, or all other bots on the Toolserver will get blocked. Also, please inform me on my talk page, so I can fix the problem.