It is ok if a battery has a higher mAh rating than the original... for the most part. Think of the mah number as how long the battery will last. In general bigger numbers are better here.
Getting in to the nitty gritty, there are cases where a badly designed product can be damaged by a battery with a much higher capacity as the charging circuit is overtaxed by a dead battery, however, as far as I am aware the circuits used in mth engines are designed to protect against excessive current draw as most every quality product is.
In short, a 200mah battery is a just fine replacement for a 170mah one, and it will last a bit longer on a charge.