How to make a bespoke itemize environment

Sometimes in beamer I like to use itemize as follows (code largely from https://topanswers.xyz/tex?q=1334):

documentclass{beamer}
setbeamersize{text margin left=10mm,text margin right=5mm} 
setbeamertemplate{frametitle}[default][center]
newenvironment{grayenv}{only{setbeamercolor{local structure}{fg=black!15}}}{}
begin{document}
begin{frame}{Frame Title}
setbeamertemplate{itemize items}[circle]
addtolength{leftmargini}{-0.7cm}
begin{itemize}[<+-|gray@+(1)->]
setlengthitemsep{5pt plus 1fill}
item line one
item line two
item<+-> line three
end{itemize}
end{frame}
end{document}

This has the effect of fading out bullet point markers for old bullet points as well as a few other features I find helpful. Notice that the final item has to have <+-> so we don’t get a new slide with all the markers gray.

Is there way to make a new environment myitemize that would capture all the features of my bespoke itemize environment?

documentclass{beamer}

setbeamersize{text margin left=10mm,text margin right=5mm} 
setbeamertemplate{frametitle}[default][center]
newenvironment{grayenv}{only{setbeamercolor{local structure}{fg=black!15}}}{}
setbeamertemplate{itemize items}[circle]

addtolength{leftmargini}{-0.7cm}

newcommand{myitemize}{itemize[<+-|gray@+(1)->]
setlengthitemsep{5pt plus 1fill}
defItem{item<+->}
}
letendmyitemizeenditemize


begin{document}
begin{frame}{Frame Title}

begin{myitemize}
item line one
item line two
Item line three
end{myitemize}

end{frame}
end{document}