A crystal's effective series resistance effect on circuit operation
It depends on your driver circuit, how much of negative resistance it provides. It is not clear in first place that the 25-Ohm crystal was selected optimally. Usually there is enough room to accommodate a range of xtals, the 25 or 40 is not much of a difference.

The other thing to care about is the circuit drive strength relative to max dissipation power in xtal. Xtals should not be over-driven, and smaller SMD  packages usually have much-much smaller limit. If your driver is NOT a 1.2 V or 1.8 V circuit with limited output impedance, the design might be in trouble.