Type K thermocouple durability in semimolten plastic
Normally a plastics T/C has a 300-series stainless steel protection tube. Depend on the thickness of that tube scraping off plastic with something softer may be acceptable. Brass tools are often used so they won't damage expensive steel molds and extrusion dies.

If you can see the glass braid it isn't going to be very durable- use the type with a robust tube and armored wire- there are thousands of different types and constructions- decently made thermocouples themselves tend to be quite tough. Chemically, the compatibility is good for most plastics.