Extend leg length

How difficult is it to modify a seat or footwells?  I have a lightweight (28 lbs) single layer fiberglass spec ski with fixed leg length. Being so light, it picks up small waves much better than newer spec weight (39 lbs) skis. It is worth near zero, so I don't want to spend too much to add 3-5 inches so my knees do not sit so high. I am very cramped, uncomfortable.  I think it was Ranga that mentioned modifying is feasible.  Would it be easier to move seat back or footwells forward?  

My first thought is that moving the seat back will change the center of gravity, so will be easier to pop over foamies and keep the nose from pearling, but harder to drop into bumps.

I'm curious if the footwells are pressing up against any kind of structural element inside the hull, or are they bonded to the bottom of the hull? 

2 of my friends have done major cockpit surgery, taking a comfortable bucket and dropping it into a different hull, so it isn't beyond the ability of a dedicated amateur, but if this was my project I would probably start by cutting a small hole just forward of the footwells, to take a look inside and see what would be involved with moving them forward, so that the boat's center of gravity stays the same.  I would think the footwells would be easier since the bottom half of the hull is designed to accept a top hull with many different sized footwells, correct?  

I think  the only real option is to move the the foot wells (heel stops) forward.
By the way, at 28 lbs this is not a true "spec ski". It could be disqualified in a USLA race for not meeting minimum weight requirement specs. The USLA or other such organizations do not want any paddler to have an unfair advantage. My first ski was from a team mate that had his ski disqualified for not meeting specs. He was winning all the races and someone complained. He got a proper spec ski and still beat everyone else. Funny, they didn't care if I paddled the disqualified ski.
At 28 lbs. it will definitely be a more fun toy in the surf though. Might be a bit more fragile.
Good luck with it.

Never adjust the seat unless that is your last and only option.
No problem for me to extend or shorten the foot wells, I do it regularly, for the lay man not so much.
Yes cutting the complete double footwell out is no problem. I usually cut both sides parallel and the piece I remove from the front to extend I add to the back, but as I said if not cut parallel  it makes it much harder. Remember you also need to add to the internal rudder tubing for the cables, I usually replace both tubes all the way to the back. And you will have to redo the rudder cables as they will not be long enough.
The concept is easy but the execution can be a lot harder.