Switch 450kW pump power supply to 500kVA generator

Normally High capacity pump motors like 450 KW are designed to start with rheostat starting (Slip ring Motors) switch gear. In recent times soft starters have come and started with low voltage starting smoothly using solid state devices. Here the question asked is can he switch over the 450 KW pump motor running with grid supply to generator supply of capacity 500 KVA with a bypass contractor.

Reduce voltage starter, as it is a least expensive method and sometimes there will be a problem during the transition from star to delta operation due to voltage dip and re-acceleration of motor.

Apart from the starting point of view, I think 500kVA generator is still not adequate for normal operation as motor rating (450kW @ 0.85 pf ) will be about 530kVA.
It is better to rate the generator at least 1.25 times of motor rating by considering the service factor.
Unless you purposely oversized the generator and are fortunate to have an engine with a bit more pf.....typically a 500kVA generator is a 400kW genset and would not be adequate.

500 KVA generator can deliver 450 KW load @ 0.85 PF if it works with 100% efficiency. The load itself being 450 KW it is not advisable to put this load on generator with any type of starting. It is better to use high voltage pump motor instead low voltage (415 V, 3-phase) motor. So that level of starting in rush current is reduced. Since the question being for existing system arrangement in-case of 3-phase 415 volts the answer is not advisable for the reasons cited above.