A child can get an aliyah [read the torah] and be a translator. He cannot repeat the Shimone Esrei or if he is a cohein in a shul of all cohanim he cannot make the bracha.

A person whose clothes are ripped can be Pores al shema and translate the reading of the torah. He cannot get an aliyah, he cannot repeat the Shimone Esrei and if he is a cohein, he cannot bless the people.

A blind person can be Pores al shema and translate the torah. R’ Yehuda says a blind person from birth cannot be Pores al shema.

Megila 4:7

A cohein that has a blemish on his hands cannot bless the people. R’ Yehuda says even if the cohein has his hands colored with woad or madder, he cannot bless the people because people will look at his hands. In the times of the Bais Hamikdash the Schenina was noticeable on the Coheins hands and it is not proper to look at it.