>>33655
Use a text editor that allows string replacing between all the open documents (for example, geany).

Alternatively, just iterate a string replace through bash.

>>33655
I use this to batch-edit MKVs.

You'll need to do a bit of modification to edit the styles instead of the text, but it should be simple enough.

http://pastebin.com/8xp8EwMX

what type of subtitles are we talking about? considering you're talking about styles, i'm guessing ass/ssa? just open them in a text editor. one of the first blocks of text defines the various styles with a name, font, size, color, etc. if you want to change the style, just edit that one line that defines the style and it will apply to all lines of that style.

here's an example i pulled out of one of my subtitles created with Aegisub (this is the third block of text):
[V4+ Styles]
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
Style: Default,Arial,36,&H00FFFFFF,&H000000FF,&H00000000,&H00000000,0,0,0,0,100,100,0,0,1,2,2,2,10,10,10,1

so if you want to change Fontsize, you'd have to edit "36" to something else.

batch replace across multiple files also works in Notepad++ (which i would call the most widely spread text edtior for Windows which a lot of people actually like).