Rewrite the phrases in Bold, using an appropriate modal and making any other necessary changes. 1. It's possible it'll rain later. It may rain later. 2. It's necessary to talk to…

Конечно! Вот переписанные фразы с использованием подходящих модальных глаголов и исправлениями при необходимости:

1. It's possible it'll rain later.
   It may rain later. (уже исправлено)

2. It's necessary to talk to the headmaster.
   You must talk to the headmaster. или It's necessary to talk to the headmaster. (можно оставить в оригинале, так как "necessary" уже выражает необходимость)

3. It's forbidden to bring pets into the classroom!
   You must not bring pets into the classroom! или It is forbidden to bring pets into the classroom! (оба варианта правильны)

4. It isn't necessary for you to finish the project by Wednesday.
   You don't have to finish the project by Wednesday. (альтернатива, более естественная в разговорной речи)

5. Always wear a uniform, it's a rule.
   You must always wear a uniform. или Wearing a uniform is a rule.

6. It's a good thing to revise for a test over the weekend.
   You should revise for the test over the weekend. или It's a good idea to revise for the test over the weekend.

7. Everybody is obliged to hand in their homework on time.
   Everybody must hand in their homework on time. или People are obliged to hand in their homework on time.

Если нужно более формальное или менее формальное оформление — дайте знать!