When you define custom macros and want them (this might not be wise in any case, since you don't want every macro to be added by every user) to appear in the RichEdit Add WebGUI macro pop-up the following file should be edited:

/data/WebGUI/www/extras/tinymce2/jscripts/tiny_mce/plugins/collateral/collateral.html *

Just add

<option value='^myMacro'>myMacro</option> 

to the selection list of your choice (Asset, User, Navigation or Style). 

* This file is not available in 7.6.7and are available in the file /data/WebGUI/www/extras/tinymce-webgui/plugins/wgmacro/macro.htm

A second gotcha is that during upgrade, this file will probably be overwritten, so you should actually make a new file with the changes and refer to this in the Rich edit files or change it every upgrade.