It isn't a big deal unless you want to use your 4 wheel drive. The rear tires, being larger, will over run the front and it is really hard on the driveline. If the size difference is really big it could make it hard to steer when in 4 wheel drive. I would say if you have to do it, pull the front drive shaft. Just my 2 cents.
With different size tires, it is similar to changing your gear ratio to a mismatched one.
As others have said, when in 4X4, it will not be synching up and your rear tires will be spinning faster then your front ones.
Bad idea really.
Technically, you could do it, but it'd have to be a permanent change and set up for it specifically.
You'd have to regear the front and rear differently, and the ratio between the gearing would have to be the ratio between the tires.
For example, 3.73 in the rear and 3.55s in the front.
3.73 / 3.55 = 1.05
33" tires * 1.05 = 34.7" tires.
Put 35" tires in the back with 3.73 gearing.
Put 33" tires in the front with 3.55 gearing.
That would be about the only way it would be possible if you wanted to still use 4 wheel drive. Quite a bit of work, it would have to be really specific, and would be a permanent change that would have to stick with the vehicle.
If its a bog only vehicle. I see a few mud bog rigs running large (38"+) boggers on the rear and will run a 35"-36" tsl on the front. but they never see street. and its not off roading, or trail riding, its straight mud boggers.