"Although this is a major upgrade version of pgModeler it is recommended NOT EXPORT the models created directly to production environments. Not all possible code generation were tested in this way, is its your own risk export the models into environments that are not intended for testing. The project's author is not responsible for any possible loss of data due the inappropriate use of this tool."
The point here is not "don't use tools". It's "test your changes". Pushing straight from a tool into production, or making the change by hand in production, or anything on the spectrum inbetween, is unwise.
After all there aren't many high quality opensource RDBMS GUIs available. The only one I know is pgAdmin and even pgAdmin has some serious bugs. (GUI freezes easily when you have many windows open and/or do large queries; import/export barely work)
The only code I would trust is the code I generate myself... ;)
DbVisualizer (http://www.dbvis.com/) is an excellent cross-platform, multi-product GUI tool. Doesn't have many design tools (well not any really, but neither does PgAdmin). Java-based and not free, which gives freeloaders and snobs something to complain about. No relationship, just someone who has been happy to be a customer for many years.
"Although this is a major upgrade version of pgModeler it is recommended NOT EXPORT the models created directly to production environments. Not all possible code generation were tested in this way, is its your own risk export the models into environments that are not intended for testing. The project's author is not responsible for any possible loss of data due the inappropriate use of this tool."
https://github.com/pgmodeler/pgmodeler#warning