Apart from the general document layout, the layout and formatting of indexes depend on two things:
The parameters of
.ist(index style) files that are used bymakeindexwhen transforming raw index data into.indfiles (which contain atheindexenvironment). These parameters control, e.g., the presence of letter headings to each index group.The definition of the
theindexenvironment which is part of document classes and may be changed by packages likeimakeidxandidxlayout. This definition controls, e.g., the number of index columns.
It is possible (although often not sensible from a typographic point of view) to change the definition of the theindex environment mid-document (e.g., "typeset[ting] a general
index in two columns and then switch[ing] to three columns for an index of names", idxlayout manual, p. 4). But is it possible to change .ist (index style) file parameters mid-document (e.g., adding letter headings for groups in some, but not in all indexes)?
EDIT: To clarify: My aim is not to switch .ist parameters within a single theindex environment, but to use different parameters (or achieve a different formatting) for several indexes within the same document.
EDIT 2: I take Martin Schröder's answer as a hint that it is possible to run makeindex "by hand" several times and to choose different .ist files each time. On the other hand, Leo Liu states in a comment that one "can add TeX boolean switches in the .ist format and modify \index to make it work", i.e., control the formatting through LaTeX macros. I'd be interested in a concrete example of a boolean switch within an .ist file.
.istformat and modify\indexto make it work, I think. Can you explain more about what you want? – Leo Liu Dec 26 '11 at 17:27makeindexorxindy. Then where is the point the format changes? – Leo Liu Dec 26 '11 at 17:29.istfile (possibly regarding the presence of letter heads)? – lockstep Dec 26 '11 at 17:53imakeidxto generate multiple indexes with different options.imakeidxsupports\write18feature to runmakeindexautomatically. – Leo Liu Dec 26 '11 at 17:59