And here's my attempt:
"To that end, he is hereby empowered to execute and sign the deed and the public and private instruments
necessary to execute
each and every listed act
herein with the particular requirements
according to the nature of each act or contract and the provisions or
special conditions that were agreed
upon according to law"
Espero que te sirva! En cuanto a tu otra pregunta, no sé si haya una manera oficial de decir lo mismo en inglés, así que esperamos para un profesional legal
