If none of the built-in styles is appropriate, you’ll probably want to
add a new style definition. Styles are kept in the vhdl-style-alist
variable, but you probably won’t want to modify this variable directly.
VHDL Mode provides a function, called vhdl-add-style, that you
can use to easily add new styles or update existing styles. This
function takes two arguments, a stylename string, and an
association list description of style customizations. If
stylename is not already in vhdl-style-alist, the new style is
added, otherwise the style already associated with stylename is
changed to the new description. This function also takes an
optional third argument, which if non-nil, automatically
institutes the new style in the current buffer.
The sample .emacs file provides a concrete example of how a new style can be added and automatically set. See Sample Init File.