Is it possible to update a contact record in an interaction during a journey. Also, can we import data into a data extension in journey builder scenarios.
Once a Contact is injected into an Interaction, if you update that record in the Event Source Data Extension, the updated values will not be applied to the Contact while they are moving through the Interaction.
Data from the Event Source DE is passed to the Interaction at the time that the Contact enters it and continues to be passed as arguments to subsequent Activities as the Contact moves through branches in the Interaction.
If you are trying to personalise email or SMS content with updated values, then you can use the AMPscript Lookup() function to retrieve rows from the Event Source DE (rather than use personalisation strings).
Regarding your question of importing data into a Data Extension, the Event can be fired at anytime while the Interaction is running. If using the Fire Event Activity in Automation Studio or the Event Schedule, then any new Contacts that have been added to the Event Source DE since it was last run will be injected into the Interaction (providing they meet the Contact Filter Criteria defined in the Event).