Internal and External .srt subtitle using different render engine ?

Is there any way to force internal .srt subtitle to render with the same engine for external .srt subtitle
because external .srt subtitle are more flexible, better quality and ...
especially for Thai languague subtitle are displayed correctly with external .srt subtitle but internal .srt not also sometime internal .srt subtitle mess up with Thai characters

 

As far as I know, no. I've asked a few times and it's never been fixed.

 

I think that would be nice. My bluray disc subtitles feels too big for me (but you adapt yourself after a while though), and it would be nice to shrink them.