I have seen ref to this, but it has always been with an open flame device,,,,,,,,,,,,,,,

Can heating of the guide be done with a soldering iron/gun without ill effects?

Why are you wanting to heat a guide? Are you talking about removing a tip top? If so, then yes, you could apply the tip of a soldering iron to the tube and remove it that way. Ideally, you'd want to maintain some pull tension on the tip top so that just as soon as the adhesive lets go the tip will come off and you won't continue heating it to the point where it might damage your blank's tip.

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Why do you want to heat the guide when you can heat the end of the glue stick in an alcohol lamp and briefly touch the guide foot to the stick and press the eye on the rod with finger pressure for a few seconds and it will set up fine. You can remove any excess glue with your finger nail before it sets up too much. If you didn't move fast enough and the glue sets up too much before you press the eye in place then you can briefly heat the foot in the flame. You will soon learn how much heat to apply to the foot by burning your fingers pressing it in place.