Is it possible to modify an existing Docker image, and how can it be done?

Yes, changes can be made to an existing Docker image. Usually, a new Dockerfile is created, in which the original image is specified as the base image, and then the necessary commands for modification are added.

Example Dockerfile:

FROM original_image:tag
RUN apt-get update && apt-get install -y new_application
COPY ./new_files /path/in/container

After that, a new image is built with the command:

docker build -t new_image:tag .

Thus, changes are not made directly to the existing image, but a new one is created based on it with the required modifications.