Hitec Servo

[Adityav95]

1) i would be pleased if someone would tell me which of these servos is the easier one to modify:
    the Hitec hs-425bb or the hs-311?

2) What is the difference or what makes the difficult to modify servo more difficult to modify than the other?

[Imignant]

there is a HiTec  Rotation Modification Difficulty List, I cant remember where I got it but I'm sure you can google it.  Lucky for you I put it into Word, the 311 gets a difficulty rating of 5 and the 425 gets a rating of 1.
Difficulty: 1 is the easiest, 10 is the hardest. 
1-3 rating: Some very slight modifications.  Trimming of plastic with a knife or dremmel.
4-6 rating: Trimming of plastic with a knife or dremmel. Drilling out of final gear/spline.
7-9 rating: Pulling or tapping out of metal pin from metal spline gear.  Possible soldering.
10 rating: Drilling out of spline gear. Trimming inner case stops. Trimming spline gear stops. Possible soldering.
anything up to 6 is pretty easy even for a beginner.
have fun