Is it possible to create sticky redirection from stdout/stderr

Is it possible to create sticky redirection from stdout/stderr

Consider such code:
echo hello >> log.txt
echo world >> log.txt
I execute command with stdout redirection. Is it possible to create sticky
redirection? Something like this:
redir stdout log.txt
echo hello
echo world
stop-redir
This would be equivalent to the first piece code.
What I really need -- make such sticky redirection for stdout and stderr
(at the same time), execute some commands, stop redirection, and read log
file.