Change Document's encoding programmatically

I am using MPF (Managed Package Framework) to create custom language service.

When I open "File -> Advanced Save Options..." in visual studio for different documents, it shows different encoding for each.

Like

for .html it is "Unicode (UTF-8 with signature) - Codepage 65001"

for .css and .js it is "Western European (Windows) - Codepage 1252"

Is there any way I can programmatically force visual studio to use "Unicode (UTF-8 without signature) - Codepage 65001" encoding for all  three types of documents?