I know a guy who tried chipping a small 9.9hp Mercury to see if it would work. It did and he got an extra 5hp.
I think when it comes to the larger more sophisticated outboards IMHO it really is not worth doing. My reason for this is that once you have bought the ECU for the larger engine (the 175 opti in your case) and paid for it to be installed, the money you would have spent could be used instead to pay the bit extra for a 150/ 175 opti with a full warranty and not a voided one, which you will be left with if you chip the 135.
This warranty is really invaluable with the 135/150/175 optis as you may have to get the power trim fixed/ replaced as this seems to be a very common problem with these engines.
Now once your engine is out of warranty and if you can get a cheap 150/175 ECU. Fire Away!! Won't affect Smartcraft gauges either as they will auto detect that a new outboard has been fitted.
Patriot, I know your 135 is brand new so I would say hold onto your warranty, or else change to a 150/175.
If In Doubt, Go Flat Out!!