You can probably change the default editor to ed and use a heredoc to edit.

EDITOR=ed
export EDITOR

crontab -e << EOF
> a
> * * * * * Myscript
> * * * * * AnotherScript
> * * * * * MoreScript
> :
> w
> q
> EOF

Note the leading > in that code means the return/enter key is pressed to create a new line.
The a means APPEND so it will not overwrite anything.
The : means you're done editing.
The w means WRITE the changes.
The q means QUIT or exit ed.
you can check it out

crontab -l

You can delete an entry too.

EDITOR=ed
export EDITOR

crontab -e << EOF
> /Myscript/
> d
> .
> w
> q
> EOF

That will delete the crontab entry with Myscript in it.
The d means delete the pattern inside the / /.
No check it again

crontab -l

This solution works inside a script too less the > of course :-)