Opening new Terminal.app window/tab with a certain profile from command-line or AppleScript?
Can you just run the startup command with do script?

tell application "Terminal"
    do script "emacs"
    set current settings of selected tab of window 1 to settings set "Grass"
end tell


If someone else doesn't need to run any startup command, you can use do script "" to open a new window:

tell application "Terminal"
    do script ""
    set current settings of selected tab of window 1 to settings set "Grass"
end tell


Or you could also use do script "" when changing default settings:

tell application "Terminal"
    set old to default settings
    set default settings to settings set "Grass"
    do script ""
    set default settings to old
    activate
end tell