You can restrict a replacement or set of changes to a single section
of a .INI file. The trick is to use a search/replace as the
restriction. The example below converts a .INI file section starting
with [TmainForm] to lowercase. This can be easily changed to perform
a search/replace, or to remove matching lines, or to add new lines
with an Add Footer filter.

EasyPattern [[ mustBeginWith( '[TmainForm]', cr, lf, ), 1+ char,
mustEndWith( cr, lf, '[' ) ]] with [$0]
| [ ] Match case
| [ ] Whole words only
| [ ] Case sensitive replace
| [X] Prompt on replace
| [ ] Skip prompt if identical
| [ ] First only
| [ ] Extract matches
| Maximum text buffer size 4096
|
+--Convert to lowercase

If the .INI file section will be longer than 4Kbytes, increase the
maximum text buffer size to suit.