You can do per session. As for the command, you would have it read the .txt file and check till is the .txt file matches. If it matches run another command, if not, then keep checking till goal is reached.
Example:
Command: !followgoalcheck
Command Message: @if@[@readfile@[C:\Deepbot - Twitch Stream Assistant\obs\FollowerTarget.txt]||50/50||Insert command here to trigger chat message and OBS Remote to enable image||@exec@[30,!followgoalcheck]]
I don't remember the exact output of the FollowerTarget.txt file, so may have to change 50/50 to whatever it should look like when the goal is met. But in my example, this would check the .txt file every 30 seconds to see if the .txt file reads 50/50 follower goal, once it reaches it, I would have it run the command to do chat message/pop up on the stream. If the goal isn't met, run the command again after 30 seconds.