I received a male normal Torchic from the Mystery Gift. Can I soft reset to try for a female and/or shiny or will it be counted as received and thus lost?
You will always receive a level 10 Male Torchic with the Speed Boost ability. The nature can be changed, but you will never get a shiny or a female. The event runs until January 15.
You can only get a shiny through events if that event is for a shiny, otherwise you will get what is described every time.
I can't find any official conformation, but other sites agree that the Torchic will be a non-shiny male and that you can save before collecting it from the delivery girl to soft reset for different nature/IV. You can also wipe your save and get the Torchic Mystery Gift again provided the event is still running.