Change some charachter in All field before saving node
You're probably looking for hook_entity_presave():


  Act on an entity before it is about to be created or updated.


It's equivalent to hook_node_presave(), but as the name suggests is run for all entity types.

From there you can use the Field Info API functions to get a list of fields that should be attached to that entity, then loop through them and do the character replacement.