First off since the power supply has the needed 2 x 6(one is a 6+2, but the 2 can be taken off) pin pci-e power connectors, You should not have to do any mods to make it work.
I am not sure why a user had to do any mods since lets say a gtx 770 is in use at MAX load it is 170 watts. Take 170/12 you get 14.16amps. This does fit within one rail.
To add to this, Multi rail power supplies are actually single rail power supplies with current limiters used to make virtual rails. This was done to avoid a user taking a 1 single power cable and y cabling it it run a full system. Most 18 amp limiters will not actually trip until about 20 amps either.
Ever since multi rail power supplies came out, they have had many users who somehow though that they had power being lost on one side and felt the need to try to find a way past something that is simply not an issue for 90% of users.
You will also see many multi rail power supplies with with rails that simply do not add up. this is because you can have 30 amps to play with and still use 2 x 18 amp rails. this just means that as long as the 2 combined do not pass 30, you are good. this also gives that little more room for a system that is not actually placing a heavy load on one rail.
Below are 2 examples of multi rail power supplies that have rails that do not add up. so you can not always add the rails.
Click \/
Spoiler
22 amps @ 12 volts vs 30 if one adds rails.
24 amps @ 12 volts vs 34 if one adds rails
Now based on other power supplies sold based on the design of yours, I think you are actually at 36amps. I just want you to know that adding rails is not always an option.
Also since Nvidia monitors cards power consumption it will not go much over 170 watts under any circumstances(well you can allow about 30% more, but I do not think you are doing that).
Either way you should keep an eye on the system to see how it functions under the new load. I know that adding specs gave me a higher power consumption than I get in normal heavy use situations.
So for my SFF Media Center
H55N USB2 this is a low powered board lets say with memory 15 watts
I5 750 rated at 95 watts
GTX 650 ti rated at 110 watts(Factor overclocked version. so it should be higher, but is infact lower). Used to have a 5770, but it took more power watching videos and that made it less ideal for this systems primary use.
1 128 gigabyte ssd for Windows and programs
1 2.5 inch 1tb(WDC Blue) hard drive Media Storage
1 3.5 inch 3tb(WDC Red) hard drive File and network storage for other systems.
2 x 120mm fans one for the cpu and one for the system intake
1 x 70 mm fan for top exhaust(Think i need to quiet this one down a bit)
Now this system is nothing near as powerful as what you have, but it also only takes about 40(drops lower at dead idle) watts at idle and 140-150 when gaming. I can get it upto about 180(that is well under the numbers posted without even including drives/fans/usb devices/ect) if I try. Simply put, you do not always need massive amounts of power to run a system. It all depends on part selection.
I will try to get some numbers from my main system later, but since it no longer has any hard drives just solid state drives. the power consumption is down.
Edit
I just want to add that this rail modding a user reported is simply using adapters to get power from another plug. like those 4 pin molex to 3 pin pci-e adapters that come with the card.On your power supply you can see what is on each rail by looking a the yellow wires. solid yellow is one rail and yellow with a black or blue stripe is the other.
Just in case you want to go this route, that is all you have to do.