Attachment - file name

I need to rename an attachment.  I want to remove all blank spaces and replace them with underscores.  I found a post from 3 years ago that asked the same question.  There was no inherent solution at the time.

In a pipeline, I can upload the file to Sharepoint and add text to the front or end of the name, but I can't inherently adjust the original name.

In the below example, I am adding a string of characters to the beginning of the name but I can't figure out how to adjust the 'File name' property of the Attachment type. 

Any suggestions on how to change the the 'File Name' attribute prior to calling a pipeline (i.e., formula-text field) or within a pipeline will be appreciated.

Thanks...Aaron