Effect of changing the length of an inverter's N-mos transistor on the propagation delay
After checking it a bit, I arrived at the following answer:

Increasing the length of the N-mos means that the current will take more time to pass the tunnel, effectively let's say that the current is lower= the resistance of the N-mos is higher. That means that the P-mos part that has a lower relative resistance would want to pull up the voltage to it, moving the VTC graph a bit to the right, since the N-mos will have to invest a larger voltage to get over the P-mos and to start pulling the voltage down. since the VTC has moved to the right, we expect that the Vil,Vih values will get bigger, but the Voh,Vol values not to change significantly. going over to the Noise Margin formula, we see that while the NMh gets lower, the NMl gets higher, and the overall Noise Margin get lower.