So, while I was asking about how headers change the font, I got to thinking. How many [sup] (or [sub], either works) brackets would it take to roughly replicate each header size as regular RPG text? I don't know who would even care about this, but if you want something that isn't unicode and breaks on certain devices, this might be for you. 

It does have some issues, though. The text doesn't like to wrap, and will turn into a garbled mess once it reaches the other end of the post/reply box. Also, it doesn't like enter gaps/multiple lines of text in general, so you'll have to input the coding per line of text to try and "get around" the previous issue. Maybe someone can improve on this, idk.

Testing font. This is a message.
0 [sup] = Regular RPG font size (without header).

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[sup][sup][sup][sup][h1]Testing font. This is a message.[/h1][/sup][/sup][/sup][/sup]
4 [sup] = normal RPG font size (with header [h1]).

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[sup][sup][sup][h2]Testing font. This is a message.[/h2][/sup][/sup][/sup]
3 [sup] = normal RPG font size (with header [h2])

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[sup][sup][h3]Testing font. This is a message.[/h3][/sup][/sup]
2 [sup] = normal RPG font size (with header [h3]).