The process of making a file is to copy and paste the frequencies into a spreadsheet for editing and then import the spreadsheet into the scanner software. The exact p=steps should be in the instructions for the software you use (Freescan, etc.). The other alternative is to type them into the software and send the files to the scanner. This works if you don't have a large number of frequencies and is not too hard since you are dealing with simple analog frequencies.
It is up to us. I recently submitted changes and new "working" repeaters for central California. At the time of my submission only a dozen were listed for 2m & 70cm. It now includes 6m and 1.25m. I have even more to submit with 33cm as well as digital variants like DMR, D-STAR, and C4FM.
If you do submit frequencies ensure you double check after it is posted. I am finding errors as well as changes to repeaters that were not done but doubled up with the correct info. Bad data is not good.