I always use fixed resistors to do vmod. Since fixed resistor is more reliable, less error prone, and not subjected to mechanical vibration and human errors (wrong turn by mistake or by little brothers or sisters, ...).
If one has some more background in electricity/electronics, get a few fixed resistors before hand, and you can play with resistors in series and parallel to get different values and tune for the final "optimal" solution.
Back to the NF7-S rev 2.0, for chipset Vdd, I used a
5 KOhm to get 1.85 V (bios setting at 1.7V)
3 KOhm to get 1.97 V (bios setting at 1.7V),
- you may adjust bios setting to adjust the Vdd if it is too high.
2 KOhm would be even higher Vdd, ...
I like to use SMD grabber, at least at the beginning stage of the vmod for experimentation.
Measure the Vdd voltage and the resistance using digital multimeter, and fine tune them accordingly. You can plot you own resistance vs Vdd characteristic.