- Normal mode completed (this is a must)
- Simulator completed (have not checked, but better safe than sorry)
- Hard mode accessible (this is a must)

Now select a relatively easy HARD mode mission (for this, I chose Hail of 
Bullets) and proceed to complete the mission, achieving initially a rank of 
LOWER THAN S.
Then, upon completion of the mission, replay the same mission, but this time, 
acquire an S-Rank on it, and you will receive your FRS point. Now you may repeat 
that mission, and for each time you S-Rank it, you will receive another FRS 
point, up to the maximum 300.
I have tested this on Regulations 1.10, and confirmed this works. Other tests 
done by other players confirm this works as well on Regulations 1.00.

This will allow players to achieve 300 FRS without having to S-Rank every hard 
mode mission.