If you do 35s, you will definitely want to regear. That is like 20+% larger tires(depending on what you started with). If you are running 3.73 stock gears, you MIGHT Get away with it for a short while. If you are running 3.07s, you will HATE it.
With all that being said, I would suggest saving a couple steps and $$$, and just doing the 35s now if you are even considering it(which you are). Money spent twice is retarded. Might cost a little more now, but in the long run it will save you a lot.