See the free Fix File Encoding extension :
The free Fix File Encoding extension prevents Visual Studio 2012/2010
from adding BOM to UTF-8 files.
Normally, when you edit a UTF-8 file in Visual Studio, it adds the
byte order mark (BOM) sequence 0xEF, 0xBB, 0xBF to the beginning of
the file. Sometimes it confuses other applications further processing
the file. You can select an encoding manually (File - Advanced Save
Options... or File - Save As... - Save with Encoding...), but you need
to do it each time you reopen the file:
Fix File Encoding automatically detects when a UTF-8 file is opened in
Visual Studio and sets its encoding to UTF-8 without signature. If you
don't edit the file, it remains unmodified. If you edit the file, it
will be saved without the BOM.
Fix File Encoding lets you configure which files to encode based on
the file path and the file extension. By default, only .html files are
protected from Visual Studio.
I have no experience with this extension, but it sounds like it answers your needs.