Betty is right. Your shortcut, while not a horrid idea, will probably not work. The problem will be that the guide feet will likely not be the same as what you are pulling off.

You can slice the thread as you mentioned on both sides of the guide and with a little sideways pressure the guide will pop off. The thread will mostly peel away with only the thread that was not on the foot remaining. That should be able to be unwound. A hair dryer can be used to soften the remaining finish as scrape that off with something like a credit card or cut a scraper out of a coffee can lid (plastic). Clean up with alcohol and you will be ready to re-wrap.

I use these little critters made from small hair ties to hold guides in place. Surgical tubing, the rubber bands used for braces or thin masking tape can also be used but these are fast and reusable! You can test cast with these holding the guides, too.