Facebook/Twitter posts SHARE button confusion

I've read on Facebook's guidelines with Share button for iOS Do's and Dont's.

Does Facebook not allow there to be a custom message by the developer when the user shares their Facebook post?

If I create the following post for example: "I just scored %i points". That %i would be depending on how many points user scored in game. Am I allowed to include this in Facebook SHARE button posts? I think Facebook said no, but I see a lot of game developers are doing it anyways.

So is it allowed or not? I think it's allowed for Twitter, uncertain for Facebook. Do you do it as a developer if you use a Facebook/Twitter SHARE button?