iTerm2 supports a custom escape code that changes the profile on the fly. Put it in your .bashrc or .bash_profile.
<esc>]50;SetProfile=X^G
where X is the profile. For instance, to change the profile to one called “Foo”, us this shell script:
#!/bin/bash
echo -e "\033]50;SetProfile=Foo\a"
To change it back when you log out, put code to change the profile back to default in ~/.bash_logout.