Replacing NTC Thermistor with an SMD Resistor

Hello masters! This is the diagram from my motherboard's PWM Controller (Richtek RT3606BC). I experience overheating flags on VRMs, even if it is not literally overheating. There are two NTC Thermistors in my motherboard, on the top side, I measured it with 68k Ohms on ambient temperature, as I put heat on it, its resistance goes down. On the bottom side, there is also an NTC Thermistor with that diagram (above). However, when I measured it, it is constant 12.09k Ohms, regardless of heat. So I suspected that I have a faulty thermistor, so I replace it with a resistor (98k Ohms), but still it shows 12.57k Ohms, so I replaced the R1 with 0.5M Ohms, and I get a constant 67k Ohms on the NTC Thermistor (Resistor) part. Am I doing this right? Hehe. Just experimenting and no advanced knowledge with this. Hehe.

It's extremely unlikely your thermistor is faulty (unless you've physically broken it), they are incredibly reliable devices. You can't read it's value in-circuit, because you also read through the other connected components - particularly R1 and R2, but also potentially the IC.

If the system thinks it's overheating, why do you think it isn't? - replacing the thermistor with a resistor will remove all protection from the VRM's, which could potentially be catastrophic.