I generally prefer the feel with 30mm's+ more travel than designed for slacker angles without any issues thus far.

Get a U-turn fork and adjust for whats the come or find what your happy with and leave it there.

Gribble,  if thats a REBA they feel alot plusher with just 15mm's more travel,  easy job,  just make sure the Circlip goes back in the same way around and the little dimple on the plastic thing above it sits in the circlips gap,  or it'll come undone.

Just because a fork has more travel, it needn't upset the balance of the bike, or void the warranty. If you get a dual air fork, you could add more negative air to get more sag, and use the extra negative travel to allow the wheel to track the ground while maintaining the same ride height and not upset the handling too much, while improving small bump response. They're usually lighter and cheaper than travel adjust versions too.

The amount of travel is less important than how you use it. It's the crown to axle measurement at the sag point that manufacturers are more worried about.

i got a 100mm fox on the back and 85mm - 130mm on the front.The bike is set up for 100mm at the front and then i just wind it open to 120 - 130 when i point it down hill,

works for me anyway.

I think finding out if the frame is warrantied for it is more important than worrying about the small change in angles (you can always run more sag to compenesate).

If the replacement fork is not too much longer you should be OK, just remember that adding a much longer fork will increase the leverage forces on the headtube of the frame; hence worth checking warranty.

And the heavier you are the less leway you have on putting on longer forks,  remember that too,  also the harder you ride.

More Sag to compensate ='s  STUPID IMHO  Don't do it!!

29'' front wheel  = STUPID IMHO  Don't do it!!

But you've never done 29",  I've done too much sag !!! 

Just check the length of the fork and how slack it makes the head angle. If you are comfortable with the slacker head angle - slower to steer therefore harder work on single track but better in rock gardens and balls out descending.  I tried to this with a Cove Handjob and realised that the bike just became unsteerable with a 120 when I should have been running with an  80 - 100.  The sag argument eludes me - why bother with a longer fork then?  Stick with a shorter travel fork.  But if the steering is ok with a longer travel then the comfort and security in a full on downhill of a degree more slack is just great. 

I agee with Dan - unlikely that the warranty would be valid.

Especially as a fork sagged out more will just bottom out and ride poorly totally whats the point,  and a RS Fork with the Negative air anywhere near the positive makes it run POORLY on rock gardens as it cushions the return too much let alone sucking it down,  sticks the fork into a higher Positive Chamber pressure Sag by increasing it,  which Lowers small bump doesn't increase it anyway.

Putting a longer fork on slackens the bikes angles,  which just forces your weight further back,  seat forward and a bars rotated forward @5mm's area makes up ( from experience )  for around 20mm's more fork travel 15mm sagged )

A  100mm fork will usually be run at 25% sag, so would leave 75mm +ve travel.

130mm forks are generally run with 30% sag, leaving 91mm +ve travel.

A difference of 16mm

This would alter the head angle by no more than half a degree. Well within most manufacturers' guidelines of +1 deg, and increase negative travel by 14mm (the size of a small root)

The higher vloume air chambers will give a slightly more linear midstroke response, but as the fork starts from deeper in the stroke and air springs tend to ramp up, the difference in bottom out will be barely noticable. The fork will dive a little more under braking, but this can be offset with low speed compression damping.

The negative chamber is so small, that once the fork is compressed by 15mm, the -ve pressure will effectively be 0. From this point on, it will have no effect on the +ve spring curve, and it doesn't affect the return rate to the sag point, as this is the function of rebound damping (some RS forks suffer with poor oil flow through the high speed rebound porting, and this usually causes the pack down and harsh feel. This is what Push tuning dials out by using a high flow piston, and speed sensitive shim stack alongside the needle & valve porting). The -ve spring will assist in stopping the fork top out though, and will hold the travel nearer the sag point, and maintain ride height ready for the next compression phase if the rebound is set correctly, allowing the wheel to track the ground better on smaller hits.