Is it safe to take a moderna vaccine as a second shot if your first shot was a pfizer covid vaccine. the reason would be shipment delayed and the need to continue to vaccinate 2nd doses to people with out delaying?

Hard to know. Since this is not the way they were tested/conditionally approved for urgent use it is hard to say this would be safe or a benefit. It might be. It might also be better to wait a few weeks or even months to get the 2nd dose of the same vaccine for long term benefit. Going off the protocol is sometimes risky.

In theory you might have a more pronounced reaction to switching the second shot. However, there is no currently recognized issue with this approach

There is lack of objective information to provide an informed opinion. It is were me, I would take the second dose from a different manufacturer than not taking the second dose. You could also take the scheduled second dose, as and when it becomes available. Wish you good health.