Add subtitles to BDMV without replacing

[NiQ]

I've noticed this guide on how to add subtitles to a Blu-Ray without losing the menus -
https://forum.doom9.org/showthread.php?t=150511

First of all I apologize for opening a new thread, but the original grew so big that it seems most people have stopped following it.

Anyway, the issue is that said guide relies on an existing subtitle stream to replace. This creates a major issue if the disc had no subtitle streams at all to begin with. Is there any way to add a new stream without replacing an existing stream?

[Emulgator]

Drag-and-drop your .srt onto tsMuxeR.
Or you add a line to your .meta like:
S_TEXT/UTF8, "D:\ENCODE\The Movie\00000 The Movie en 1 23,976fps.srt",default=all,font-name="Verdana",font-size=50,font-color=0xff78c8f0,bottom-offset=24,font-border=5,text-align=center,video-width=1920,video-height=1080,fps=23.976, lang=eng
This will make the new subtitle stream the default stream.