Is there any way to reuse step across Bitrise workflows? For example, let's say I have script step with bunch of shell script in it. I do not want to create my "own" full-grown step. The script is changing something in codebase and the changes will further be used by other steps of given workflow.
If you plan to use it across many apps the best solution is to convert it to a step - if you already have it as a script it's really simple using the bitrise CLI (bitrise :step create). That way you can version it and you can manage when a given workflow is updated to the new version.
If you don't want to do that, you can use the Remote Bash Script Runner https://www.bitrise.io/integrations/steps/remote-script-runner step to run your script from a URL (e.g. from a secret GitHub Gist).
Alternatively you can also include your script in your repository, and then run that from a Script step or via the Script Runner step (https://www.bitrise.io/integrations/steps/script-runner).
There's also an unofficial step to run a script from a private github repo: https://www.bitrise.io/integrations/steps/github-script-runner