Can you change the file metadata on a cloud database using Apache Beam? From what I understand, Beam is used to set up dataflow pipelines for Google Dataflow. But is it possible to use Beam to change the metadata if you have the necessary changes in a CSV file without setting up and running an entire new pipeline? If it is possible, how do you do it?
You could code Cloud Dataflow to handle this but I would not. A simple GCE instance would be easier to develop and run the job. An even better choice might be UDF (see below).
There are some guidelines for when Cloud Dataflow is appropriate:

Your data is not tabular and you can not use SQL to do the analysis.
Large portions of the job are parallel -- in other words, you can process different subsets of the data on different machines.
Your logic involves custom functions, iterations, etc...
The distribution of the work varies across your data subsets.

Since your task involves modifying a database, I am assuming a SQL database, it would be much easier and faster to write a UDF to process and modify the database.
Change file metadata using Apache Beam on a cloud database?