It sounds like what you want is a simple manually-triggered batch program that will read a range of Modbus/TCP registers and store them in a file on demand, and then do the reverse to write them from the file to the PLC on demand.
Is that correct ?
How much programming do you want to do, and in what languages are you comfortable programming ?
What storage file format do you prefer ? The options I would guess are a CSV text file, or an SQL database table, or an Excel spreadsheet.
There's going to be a tradeoff between cost and effort, of course. Some folks would be happy with Excel and VBA. Some will grab a Python library and an SQL table. Others will buy a scripting Modbus tool like Aggsoft's data logger.