I build rods and do a fair amount of repair. I only heat tip guides, and just a little. For regular guides, lay your razor or exacto knife flat on top of the guide food, and shave toward the guide. Make sure to keep it flat and not dig. The first pass, you will probably only shave some of the epoxy, but then you will shave the thread from on top of the guide foot.
Then, you should be able to peel the rest of the epoxy and thread off. After that, soak a piece of cloth or paper towen in isopropyl alcohol and soak the remaining epoxy and then lay your razor flat and carefully shave a line in it. Then peel that off.
If you are careful, you will get it all off without leaving a trace. If you are putting another guide in it's place, any scuffs will be covered, but be careful, and it will go fine.
You CAN heat epoxy, you just need to be very careful. I stopped doing that a long time ago, except for tip guides, as previously stated.