Does the ignition point of flammable substances changes when provided a pure oxygen atmosphere?
No, but because of a technical point. 

From Wikipedia: The autoignition temperature or kindling point of a substance is the lowest temperature at which it will spontaneously ignite in normal atmosphere without an external source of ignition, such as a flame or spark.

So the definition of the autoignition temperature is based on air not pure oxygen.

For the ignition temperature in general the Wikipedia reference goes on: The temperature at which a chemical will ignite decreases as the pressure or oxygen concentration increases.