The default Keynote file is at C:\ProgramData\Autodesk\RAC 2011\Imperial Library\RevitKeynotes_Imperial.txt
The Help says "Changes made to the keynote table are not available in the current project session of Revit Architecture" but that's not true, I could just Browse for Keynote File again and the keynotes were updated.
Keynote format -- from Revit's Help:
Keynotes are defined in a tab-delimited text file. The first portion of the text file is reserved for major headings/categories (the parent values). The remainder of the file is for sub-headings/categories (the child values). A tab-delimited file requires the use of the Tab key to create spaces between data entries.
Changes made to the keynote table are not available in the current project session of Revit Architecture. Changes are available when the project is closed and reopened.
You can use Microsoft® Excel or a similar spreadsheet application to manage the data, then export it to a tab-delimited file format.
Sample Keynote Text File
CSI Main Category/Heading (parent value)
11000 [tab] Division 11 - Equipment
CSI Master format sSb-Category/Heading [tab] Sub-Category/Heading Description [tab] CSI Masterformat Main Category/Heading Value (parent value)
11060 [tab] Theater and Stage Equipment [tab] 11000
11061 [tab] Acoustical Shells [tab] 11000
For sub-categories of sub-categories
11060.A1 [tab] Counter-Weight Rigging [tab] 11060
Sample User Keynote Text File
For User Keynotes you can place them in front of the CSI structure by using the following format:
Main/Heading/Parent Category
00000 [tab] Division 00 - User Notes
Sub-Category/Heading/Child
00001 [tab] User Note 1 [tab] 00000
00002 [tab] User Note 2 [tab] 00000
For sub-categories of sub-categories
00001.A1 [tab] User Note 1a [tab] 00001
