Current behavior: 
At the moment, our Update Source feature works the way that the file import settings cannot be changed, therefore the new parts of the file are uploaded with the same settings as the original file. 

Requested behavior: 
Make it possible to change the file import settings when using Update Source feature. Or at least some parts - like Regexp within Convert to Phrase TMS tags field.

Use case:
It would be useful when the file is big and used on a long-term basis. The only way to use the new settings is to upload the whole file again. However, that causes the bigger wordcount in the client's account.