Docker container environment variable file during runtime

Question

I have a docker image that basically schedules a cron job at a frequency defined when building the image using the below.

COPY myjobtime /etc/cron.d/myjobtime
RUN chmod 0644 /etc/cron.d/myjobtime &&\
    crontab /etc/cron.d/myjobtime
CMD cron 

I have the cron entry in the file myjobtime.

*/10 * * * * /usr/local/bin/sh /app/myscript.py

I would like to be able to pass the cron schedule during the runtime. Meaning, if someone wants to modify the cron schedule to a different frequency, they should be able to do that while running the container and passing an environment variable file with the new cron schedule in it. Can this be done?