If necessary, you add the entry for dialog.tlk with TSLPatcher and then you simply edit the StringRef in the appropriate global.jrl entry. global.jrl is a standard gff file, so you can edit it with your gff-editor and then use TSLPatcher's compare function to create the installer.
I don't know but I would guess that he added these strings to dialog.tlk and then changed the description to those new StringRefs. But then again, I might just be wrong about all of this.
Well, technically Fairstrides walked me through the entire process, but that's exactly what I did for the mod. I created a bunch of Strings for the new descriptions and then injected them into the GFF files and added them to Append.tlk. I believe the TSLPatcher doesn't actually edit the Dialog.tlk, but rather uses the Append.tlk to add entries. (I'm not sure about the technicals, but there are certain to be others on DS who could tell you more)