There is not a way to get the field keys programmatically by the field name if they do not already exist. At least not easily.
There is a round-a-bout way to do this. There is a function in ACF, acf_get_field_groups(). This function takes arguments. I don’t remember the specifics, but the last time I looked at it I was able to get field groups based on the post ID. You can then loop over the field groups and get the fields in each groups using the function acf_get_fields(). Then you could loop over all of the fields and find the field name and get its key.
When working with repeaters you must use keys for the repeater and all of its sub fields.
