Your comments

You can already rename a file: open the file, then go to the file properties popover and tap on the file name.
Well, it currently looks like this in Info.plist:

<key>UIAppFonts</key>
<array>
<string>DejaVuSansMono.ttf</string>
<string>luximr.ttf</string>
<string>monof55.ttf</string>
</array>

If I don't register the font files here, they are not available in the app.

You can look up UIAppFonts in the docs.
As far as I know, I have to register fonts in the info.plist file.
This can't be changed after it is in the App Store. So, if I'm
not mistaken, I don't think this would be possible.
The font is under the OFL - http://scripts.sil.org/OFL - I just had a look at it and it looks like I can use it in Textastic.

I'll try it on the iPad.
Looks like this should be possible. I'll try it and see if it works on the iPad.

• Can I redistribute ProFont Distribution?

“ProFont Distribution” is Copyright © 1997, SQ Software. The ProFont fonts are Copyright © 1997, Carl R. Osterwald. It is our intention that “ProFont Distribution” get the widest possible distribution. You may redistribute unmodified copies of “ProFont Distriubtion” as long as it is accompanied by an unmodified copy of “About ProFont Distribution 2.2” (this file). You may not charge anyone money for the “ProFont Distribution” package itself. The “ProFont Distribution” package can be distributed for free along with products for which you do charge money. The “ProFont Distribution” package can also be distributed for free as part of collections of more than 10 third party products sold as a collection (such as on the Apprentice CD series). If you do distribute “ProFont Distribution” along with another product or as part of a collection, Stephen C. Gilardi and Carl R. Osterwald would appreciate very much each receiving a complimentary copy of the whole distribution (e.g., any CD-ROM it appears on), but this is not a requirement. If you have questions about redistribution, please contact Stephen C. Gilardi at squeegee@usa.net.
If you can send me the clojure.plist file to support@textasticapp.com I'll be sure to add it to Textastic!
I don't plan to release it for iPhone right now. Maybe in the future.
This should be easy. But, I didn't think it would make a lot of sense for long source code files. I was probably wrong :)
Ok, that's easy. I'll be sure to register the .textile file extension for this.