write to a field for all entries selected

I am working on a form that "batches" entries.  I want the user to use a repeating field to add the entries they want to batch (essentially  mark as "batched" on submit)  What I need is to be able to change the appropriate field in the entries for all of those entries they have selected.  For each entry "id" chosen,  add "batched" to an empty field or hidden field in the form. (or change a radio button entry option would suffice)  this will be used to filter entries that have been billed/invoiced already.

I have been pouring through documentation and have found a method for changing an entry to another choice (radio button) from the front end but sure how to get it to work for several IDs at once on "Submit".

Ideas or point to a an action hook I might use in this situation would be most helpful.

Thanks