I'm working on updating JSON file and have following questions :
1) How do I update "Drafted By" info for each player? I tried columns "DraftRound", "DraftPick" & "DraftSeason" but after loading up the game it still shows "Undrafted".
2) Could you provide a team list with corresponding numbers? For example Buffalo Bills - 1, NE - 2...etc. I need this info for "Team" column.
3) Similar to above but for "PlayerTraits" column.
4) Is PlayerFlag only for running QB ?
5) Is it possible to edit "Social Type" via JSON file ?
6) When I go to Player's Card under Player Skills my starting QB has 66 rating for QB position. How come? Shouldn't be 99? Why so low?
7) In the column "Potential". If I fill it up only for some players will the game assign random number for the rest of them?

You don't set drafted by... that gets set by game when a player is drafted.
The team column is set based on the team id in the Teams.xml file which depends on which league format you're using
Player traits are https://wolverinestudios.freshdesk.com/ ... rait-guide
PlayerFlag is only RunningQB at the moment... other traits are handled by traits.
Social Type is not moddable at the moment
Skills are set in the import, but also can be adjusted by the game depending on if you import draft kids or import free agents, etc.
Potential isn't used during import/export and can be ignored.

As a side note there are already mods out there that you can probably look at for guidance. (viewtopic.php?f=285&t=29541)