Multiple Day & Technician Invoicing from Mobile Applicaiton

I've got a question related to mobile invoicing for jobs that take multiple days to finish. Our company services private well water pump systems. It is common to have to troubleshoot these systems and then return another day to replace components or entire systems. As a result, we regularly have dispatches that result in some type of follow up needed. To keep these jobs from falling through the cracks, so to speak, we're considering using a new status code that transfers the dispatch to a non-tech column, "Follow Up." My understanding is this new status code must mimic the "Complete" status code in order to properly remove it from our technician's tablet. Our office would then reuse the dispatch the second day by assigning a new technician to it. 

Our technicians also invoice from the field. Customers, however, generally prefer to pay one invoice. Because of this, we'd like to be able to have our first technician (who performs the troubleshoot) create an invoice that our second technician on a different day (who performs, say, a system replacement) could add to. Best I can tell, because the first technician has to use a status code that mimics "Complete" the second technician will not be able to add to that invoice as it will be read-only. 

In sum, we're trying to basically automate our follow-up process via status code transfers while being able to use and update the same invoice throughout the entire job. Has anyone else encountered this issue? Any possible work-arounds? 

Thanks!