Would it be possible to somehow input a (or multiple) tribe(s) and basically send friend requests to all members of that tribe?
If you mean to have like a dropdown where you select a tribe/s and then automatically all the tribe members in the tribe/s get sent a friend request, then no this is not possible.
If you mean to have like a dropdown where you select a tribe/s and then you manually request for friendship for all the tribe members this technically should be doable.
While technically could be doable I am not going to work on this. The idea of the script is to be used usually during the start of a world, when you add everyone as a friend just for the achievement. For that, there is no need to know if the player you are adding as a friend is in your tribe or an enemy tribe, etc. You just add it because you will remove it later on (if you want to do that later on).
I don't see the point on working on a tribe filter since this is such a specific script and will be used mostly at the start of the world for the very reason I explained above.